eventpoll.h: wrap casts in () properly

When importing the latest copy of the kernel headers into Bionic,
Christpher and Elliott noticed that the eventpoll.h casts were not
wrapped in ().  As it is, clang complains about macros without
surrounding (), so this makes it a pain for userspace tools.

So fix it up by adding another () pair, and make them line up purty by
using tabs.

Fixes: 65aaf87b ("add EPOLLNVAL, annotate EPOLL... and event_poll->event")
Reported-by: Christopher Ferris <cferris@google.com>
Reported-by: Elliott Hughes <enh@google.com>
Cc: stable <stable@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>