Using __typeof__(*ptr) on a pointer to const makes the __x variable in
__get_user const as well.  The latest gcc will refuse to write to it.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>