px4_sem: set errno, return -1 on any error
px4_sem: set errno, return -1 on any error

- Don't duplicate the ret variable to err.
- Return -1 on any error, 0 otherwise.
- Set errno to return value of pthread_cond_timedwait.

mje-nz/PX4-Firmware,PX4/Firmware,krbeverx/Firmware,dagar/Firmware,krbeverx/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,acfloria/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,acfloria/Firmware,krbeverx/Firmware,dagar/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,PX4/Firmware,PX4/Firmware,dagar/Firmware,acfloria/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,PX4/Firmware