staging: iio: isl29018: made error handling consistent

staging: iio: isl29018: made error handling consistent

Changed the processing of IIO_CHAN_INFO_INT_TIME in isl29018_write_raw()
to unlock the mutex and return at the end of the function if invalid
input is passed in. This makes the error handling code consistent with
the processing of IIO_CHAN_INFO_CALIBSCALE and IIO_CHAN_INFO_SCALE
within the same function.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>