ARM: compat: remove KERNEL_DS usage in sys_oabi_epoll_ctl()

We no longer need to switch to KERNEL_DS mode in sys_oabi_epoll_ctl()
as we can use do_epoll_ctl() to avoid the additional copy.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>