drm/i915/display: Convert i9xx_pipe_crc_auto_source to void

Convert function i9xx_pipe_crc_auto_source() to return void instead
of int since the current implementation always returns 0 to the caller.
Issue identified using returnvar Coccinelle semantic patch.

$ make coccicheck COCCI=scripts/coccinelle/misc/returnvar.cocci \
M=drivers/gpu/drm/i915/

Signed-off-by: Deepak R Varma <drv@mailo.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/Y8K2SS/zNiPAmLsS@ubun2204.myguest.virtualbox.org