media: imx-media-utils: fix a warning

The logic at find_format() is a little bit confusing even for
humans, and it tricks static code analyzers:

	drivers/staging/media/imx/imx-media-utils.c:259 find_format() error: buffer overflow 'array' 14 <= 20

Rewrite the logic in a way that it makes it clearer to understand,
while prevent static analyzers to produce false positives.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>