media: omap3isp: Destroy CSI-2 phy mutexes in error and module removal

The CSI-2 phy driver did initialise mutexes in its init function but there
was no corresponding cleanup function destroying them. Fix that. Also
clean up ISP module initialisation a little.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>