alpha: invoke oom-killer from page fault

As explained in commit 1c0fe6e3, we want to call the architecture
independent oom killer when getting an unexplained OOM from
handle_mm_fault, rather than simply killing current.

[mattst88: kill now unused 'survive' label]
Cc: linux-alpha@vger.kernel.org
Cc: Richard Henderson <rth@twiddle.net>
Cc: linux-arch@vger.kernel.org
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>