mfd: remove use of __devinitconst

CONFIG_HOTPLUG is going away as an option so __devinitconst is no
longer needed.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>