media: staging: media/atomisp: use max() impl

fix a coccinelle warning by replacing opencoded max()
implementation with max()

WARNING opportunity for max()

Link: https://lore.kernel.org/linux-media/YrNFpF2qvTxpZP8e@karthik-strix-linux.karthek.com


Signed-off-by: Karthik Alapati <mail@karthek.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>