signals: eventpoll: set ->saved_sigmask at the start
task_struct->saved_sigmask has no meaning unless we return with
set_restore_sigmask() and nobody except current can use it.
This means that sys_epoll_pwait() doesn't need to save ->blocked
into the local var and then memcopy it into ->saved_sigmask, we
can simply set ->saved_sigmask right before set_current_blocked().
Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Eric Wong <normalperson@yhbt.net> Cc: Jason Baron <jbaron@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>