staging: sm7xxfb: rename sm712_set_timing to sm7xx_set_timing

sm712_set_timing handles timing for 0x710, 0x712 and 0x720 chips. This
patch renames the name of the function of sm712_set_timing to
sm7xx_set_timing.

Tested with SM712.

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>