HID: fix build failure in hiddev_ioctl with gcc 3.2

Fix build failure in hiddev_ioctl with gcc 3.2:
http://bugzilla.kernel.org/show_bug.cgi?id=10121



The trick is to move the handling of ioctls which need to allocate
memory to separate functions.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>