staging: iio: tsl2x7x: convert mutex_trylock() to mutex_lock()

The driver uses mutex_lock() and mutex_trylock() in several places.
Convert the mutex_trylock() to mutex_lock() for consistency with other
IIO light drivers in mainline.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>