epoll: fix size check in epoll_create()

Fix a size check WRT the manual pages.  This was inadvertently broken by
commit 9fe5ad9c

 ("flag parameters
add-on: remove epoll_create size param").

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <Hiroyuki.Mach@gmail.com>
Cc: rohit verma <rohit.170309@gmail.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>