media: v4l: vsp1: Fix mask creation for MULT_ALPHA_RATIO

Due to a typo, the mask was destroyed by a comparison instead of a bit
shift. No regression since the mask has not been used yet.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>