mfd: Fix resource reclaim in pcf50633_remove()

Calling sysfs_remove_group() to remove sysfs entries
and unregister bl_pdev in pcf50633_remove().

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Harald Welte <laforge@gnumonks.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>