media: venus: venc: Fix potential null pointer dereference on pointer fmt

Currently the call to find_format can potentially return a NULL to
fmt and the nullpointer is later dereferenced on the assignment of
pixmp->num_planes = fmt->num_planes. Fix this by adding a NULL pointer
check and returning NULL for the failure case.

Addresses-Coverity: ("Dereference null return")

Fixes: aaaa93eda64b ("[media] media: venus: venc: add video encoder files")
Signed-off-by: Colin Ian King <[e-mail]>
Signed-off-by: Stanimir Varbanov <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/qcom/venus/venc.c

···
 		else
 			return NULL;
 		fmt = find_format(inst, pixmp->pixelformat, f->type);
+		if (!fmt)
+			return NULL;
 	}
 
 	pixmp->width = clamp(pixmp->width, frame_width_min(inst),