ARM: 9111/1: oabi-compat: rework fcntl64() emulation

This is one of the last users of get_fs(), and this is fairly easy to
change, since the infrastructure for it is already there.

The replacement here is essentially a copy of the existing fcntl64()
syscall entry function.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>