media: ngene: Replace semaphore i2c_switch_mutex with mutex

The semaphore 'i2c_switch_mutex' is used as a simple mutex, so
it should be written as one. Semaphores are going away in the future.

Signed-off-by: Binoy Jayan <binoy.jayan@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>