[PARISC] fix missing TAINT_WARN problem

Al viro broke us with

commit edd63a27
Author: Al Viro <viro@zeniv.linux.org.uk>
Date:   Fri Apr 27 13:42:45 2012 -0400

    set_restore_sigmask() is never called without SIGPENDING (and never should be)

Although it's pretty much our fault since parisc's asm/bug.h uses
BUGWARN_TAINT but doesn't include the file that defines it.  Fix that.

Signed-off-by: James Bottomley <JBottomley@Parallels.com>