m68k,nommu: add missing __user in uaccess' __ptr() macro

The assembly for __get_user() & __put_user() uses a macro, __ptr(),
to cast the pointer to 'unsigned long *' but the pointer is always
a __user one and so this cast creates a lot of warnings when using
Sparse.

So, change to the cast to 'unsigned long __user *'.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>