media: imx: imx7-media-csi: Remove a useless include

<linux/gcd.h> is not needed for this driver. Remove the corresponding
 #include.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>