Fix SSP descriptor documentation

[fabiensanglard]

Sorry about the extra =. This was an oversight.

[Youw]

LGTM

[tormodvolden]

I'll copy what I wrote in #1429 (comment), with updated comments:

Doxygen warnings (seen when running make -C doc) caused by this commit:

libusb/descriptor.c:1012: warning: Compound internal_ssplus_capability_descriptor is not documented.
Maybe it needs to be moved? EDIT: Last resort would be masking it with doxygen @cond conditionals. Any other suggestions?

libusb/libusb.h:1077: warning: unable to resolve reference to 'libusb_ssplus_usb_device_capability_descriptor.numSublinkSpeedAttributes=' for \ref command
Caused by the trailing =. What was the intention with those =? EDIT: FIXED

libusb/descriptor.c:1013: warning: Member bLength (variable) of struct internal_ssplus_capability_descriptor is not documented.
libusb/descriptor.c:1014: warning: Member bDescriptorType (variable) of struct internal_ssplus_capability_descriptor is not documented.
libusb/descriptor.c:1015: warning: Member bDevCapabilityType (variable) of struct internal_ssplus_capability_descriptor is not documented.
libusb/descriptor.c:1016: warning: Member bReserved (variable) of struct internal_ssplus_capability_descriptor is not documented.
libusb/descriptor.c:1017: warning: Member bmAttributes (variable) of struct internal_ssplus_capability_descriptor is not documented.
libusb/descriptor.c:1018: warning: Member wFunctionalitySupport (variable) of struct internal_ssplus_capability_descriptor is not documented.
libusb/descriptor.c:1019: warning: Member wReserved (variable) of struct internal_ssplus_capability_descriptor is not documented.

Should they be added? EDIT: Related to first point, probably one solution for all.

libusb/libusb.h:1077: warning: unable to resolve reference to 'libusb_ssplus_usb_device_capability_descriptor.numSublinkSpeedAttributes=' for \ref command

Caused by the trailing = . EDIT: FIXED

[tormodvolden]

Please see the commit I added for the @cond@ alternative. Also any other doxygen fans out there, I would be glad if someone can suggest a prettier way to do it. I know you can prepend \internal to the tag, but then you still need to document all the members.

See also my draft PR #1549 where I investigate adding doxygen validation to the CI.

[fabiensanglard]

Thank you for fixing this :), I am still ramping up on Doxygene !

I'll be more thorough in my next contribution.