mn10300: fix "pull clearing RESTORE_SIGMASK into block_sigmask()" fallout

Commit a610d6e6 ("pull clearing RESTORE_SIGMASK into
block_sigmask()") caused:

  arch/mn10300/kernel/signal.c: In function 'handle_signal':
  arch/mn10300/kernel/signal.c:462:3: warning: 'return' with no value, in function returning non-void [-Wreturn-type]

Add the missing return values, and restore the indentation while we're
at it.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>