HID: magicmouse: Correct parsing of large X and Y motions.

The X and Y values have two more significant bits in the same byte
that contains click status.  Include these in the reported value.
Thanks to Iain Hibbert of NetBSD for pointing this out.

Signed-off-by: Michael Poole <mdpoole@troilus.org>
Acked-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>