Make SPI clock pin optional for use with WS2812

smart-leds-rs uses SPI without clock for controlling WS2812 LEDs.

nrf-hal-common/src/spi.rs

@@ -93,10 +93,14 @@ where
 
  #[cfg(feature = "51")]
  fn set_pins(spi: &mut T, pins: Pins) {
- spi.pselsck
- .write(|w| unsafe { w.bits(pins.sck.pin().into()) });
-
- // Optional pins.
+ spi.pselsck.write(|w| unsafe {
+ if let Some(ref pin) = pins.sck {
+ w.bits(pin.pin().into())
+ } else {
+ // Disconnect
+ w.bits(0xFFFFFFFF)
+ }
+ });
  spi.pselmosi.write(|w| unsafe {
  if let Some(ref pin) = pins.mosi {
  w.bits(pin.pin().into())
@@ -118,11 +122,9 @@ where
 
  #[cfg(not(feature = "51"))]
  fn set_pins(spi: &mut T, pins: Pins) {
- spi.psel
- .sck
- .write(|w| unsafe { w.bits(pins.sck.pin().into()) });
-
- // Optional pins.
+ if let Some(ref pin) = pins.sck {
+ spi.psel.sck.write(|w| unsafe { w.bits(pin.pin().into()) });
+ }
  if let Some(ref pin) = pins.mosi {
  spi.psel.mosi.write(|w| unsafe { w.bits(pin.pin().into()) });
  }
@@ -140,7 +142,9 @@ where
 /// GPIO pins for SPI interface.
 pub struct Pins {
  /// SPI clock.
- pub sck: Pin<Output<PushPull>>,
+ ///
+ /// None if unused.
+ pub sck: Option<Pin<Output<PushPull>>>,
 
  /// MOSI Master out, slave in.
  ///