media: atmel: atmel-isc: fix and cleanup potential bugs

Fixed issues that can lead to potential bugs.
Cleanup order in the driver
Taking into consideration std control creation can fail
mutex_destroy call
changing controller_formats with const specifier
some cosmetic cleanups

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>