Fix up more fallout form alpha signal cleanups

Commit c52c2ddc ("alpha: switch osf_sigprocmask() to use of
sigprocmask()") had several problems.  The more obvious compile issues
got fixed in commit 0f44fbd2 ("alpha: fix compile problem in
arch/alpha/kernel/signal.c"), but it also caused a regression.

Since _BLOCKABLE is already the set of signals that can be blocked, the
code should do "newmask & _BLOCKABLE" rather than inverting _BLOCKABLE
before masking.
Reported-by: Michael Cree <mcree@orcon.net.nz>
Patch-by: Al Viro <viro@zeniv.linux.org.uk>
Patch-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/kernel/signal.c

@@ -48,7 +48,7 @@ SYSCALL_DEFINE2(osf_sigprocmask, int, how, unsigned long, newmask)
 	sigset_t mask;
 	unsigned long res;
 
-	siginitset(&mask, newmask & ~_BLOCKABLE);
+	siginitset(&mask, newmask & _BLOCKABLE);
 	res = sigprocmask(how, &mask, &oldmask);
 	if (!res) {
 		force_successful_syscall_return();