parisc: Avoid compiler warnings with access_ok()

Commit 09b871ff (parisc: Define access_ok() as macro) missed to mark uaddr
as used, which then gives compiler warnings about unused variables.

Fix it by comparing uaddr to uaddr which then gets optimized away by the
compiler.

Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 09b871ff ("parisc: Define access_ok() as macro")