CVE-2026-31603 staging: sm750fb: fix division by zero in ps_to_hz()

In the Linux kernel, the following vulnerability has been resolved: staging: sm750fb: fix division by zero in pstohz pstohz is called from hwsm750crtcsetmode without validating that pixclock is non-zero. A zero pixclock passed via FBIOPUTVSCREENINFO causes a division by zero. Fix by rejecting zer...