iio: bmc150: exit early if event / trigger state is not changed

Previous of this patch the check was only done if we enabled the event
and it was already enabled. We can do the same if the event is
disabled and we want to disable it.

The patch also adds the same check on the trigger code.

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>