media: mt9v111: avoid going past the buffer

As warned by smatch:
	drivers/media/i2c/mt9v111.c:854 mt9v111_enum_frame_size() error: buffer overflow 'mt9v111_frame_sizes' 5 <= 5
	drivers/media/i2c/mt9v111.c:855 mt9v111_enum_frame_size() error: buffer overflow 'mt9v111_frame_sizes' 5 <= 5
	drivers/media/i2c/mt9v111.c:856 mt9v111_enum_frame_size() error: buffer overflow 'mt9v111_frame_sizes' 5 <= 5
	drivers/media/i2c/mt9v111.c:857 mt9v111_enum_frame_size() error: buffer overflow 'mt9v111_frame_sizes' 5 <= 5

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>