drm: mali-dp: Uninitialized variable in malidp_se_check_scaling()

We use "mc" without initializing it if scaling is not necessary.

Fixes: 28ce675b ("drm: mali-dp: Add plane upscaling support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Mihail Atanassov <Mihail.Atanassov@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>