fix compiler warnings - SmartAudio CMS menu FREQ, POR FREQ

[nerdCopter]

fixes:

./src/main/cms/cms.c: In function 'cmsDrawMenuEntry':
./src/main/cms/cms.c:332:30: warning: cast between incompatible function types from 'CMSEntryFuncPtr' {aka 'long int (* const)(struct displayPort_s *, const void *)'} to 'char * (*)(void)' [-Wcast-function-type]
  332 |                 char *str = ((CMSMenuOptFuncPtr)p->func)();
      |                              ^
./src/main/cms/cms_menu_vtx_smartaudio.c:495:32: warning: cast between incompatible function types from 'char * (*)(void)' to 'long int (*)(displayPort_t *, const void *)' {aka 'long int (*)(struct displayPort_s *, const void *)'} [-Wcast-function-type]
  495 |     { "POR FREQ",  OME_Submenu, (CMSEntryFuncPtr)saCmsORFreqGetString, &saCmsMenuPORFreq,                                   OPTSTRING },
      |                                ^
./src/main/cms/cms_menu_vtx_smartaudio.c:537:28: warning: cast between incompatible function types from 'char * (*)(void)' to 'long int (*)(displayPort_t *, const void *)' {aka 'long int (*)(struct displayPort_s *, const void *)'} [-Wcast-function-type]
  537 |     { "FREQ",   OME_Submenu, (CMSEntryFuncPtr)saCmsUserFreqGetString,  &saCmsMenuUserFreq, OPTSTRING },

[nerdCopter]

• confirmed OSD menu items for SA/FREQ SA/POR FREQ working.
• when setup for freq rather than band/channel, i somtimes get lost signal. both master and this PR. so no change in behavior