iio: ltr501: Fix proximity threshold boundary check

Currently, proximity sensor boundary check is done
inside the switch block but outside the case
statement.Since this code will never get executed,
moved the check outside the switch case statement.

   867          case IIO_PROXIMITY:
   868                  switch (dir) {
   // Following line has been moved outside the switch block.
   869                  if (val > LTR501_PS_THRESH_MASK)
   870                          return -EINVAL;
   871                  case IIO_EV_DIR_RISING:

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>