maple: Drop unused prototypes from linux/maple.h.

This patch removes the now unneeded registration check variable from
struct maple_device. (This patch assumes the include/linux/maple.h file
has already been patched for whitespace errors by
http://lkml.org/lkml/2008/2/6/327)

Signed-off-by: Adrian McMenamin <adrian@mcmen.demon.co.uk>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>