media: ov13858: Fix initial expsoure max

Previously, initial exposure max was set incorrectly to (0x7fff - 8).
Now, limit exposure max to current resolution (VTS - 8).

Signed-off-by: Chiranjeevi Rapolu <chiranjeevi.rapolu@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>