regulator: da903x: add missing __devexit_p()

The remove function uses __devexit, so the .remove assignment needs
__devexit_p() to fix a build error with hotplug disabled.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
CC: Liam Girdwood <lrg@slimlogic.co.uk>
CC: Mike Rapoport <mike@compulab.co.il>
CC: Eric Miao <eric.miao@marvell.com>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>