asm-generic: uaccess: fix up local access_ok() usage

There's no reason that I can see to use the short __access_ok() form
directly when the access_ok() is clearer in intent and for most people,
expands to the same C code (i.e. always specify the first field -- access
type).  Not all no-mmu systems lack memory protection, so the read/write
could feasibly be checked.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>