staging: sm750fb: return -ETIMEDOUT on timeout in de_wait functions

staging: sm750fb: return -ETIMEDOUT on timeout in de_wait functions

The hw_sm750le_de_wait() and hw_sm750_de_wait() functions return -1
when a timeout occurs. Replace these with -ETIMEDOUT to use a proper
errno value and better describe the error condition.

All callers check the return value as non-zero, so this change does
not alter existing behavior.

Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
Link: https://patch.msgid.link/20260427054657.758-2-dennylin0707@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>