mfd: adp5520: Restore mode bits on resume

The adp5520 unfortunately also clears the BL_EN bit when the nSTNDBY bit is
cleared. So we need to make sure to restore it during resume if it was set
before suspend.

Cc: stable@vger.kernel.org
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>