media: ov5640: report correct frame rate to user

In commit 3145efcd ("media: ov5640: Rework timings programming"),
it defines max_fps field in ov5640_mode_info structure to store maximum
frame rate supported by each mode. But in ov5640_try_frame_interval(), it
assumes the maximum frame rate supported by all modes is 60. But actually,
only VGA support it. For others, the maximum frame rate supported is 30.
So correct it by taking the maximum frame rate supported by each mode as
the initialization value of the local variable maxfps.

Signed-off-by: Guoniu.zhou <guoniu.zhou@nxp.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>