um: don't restore current->blocked on error

If we fail to setup the signal stack frame then we don't need to restore
current->blocked because it is not modified by setup_signal_stack_*.

Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Richard Weinberger <richard@nod.at>
Tested-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --cc arch/um/kernel/signal.c
Simple merge