fs/cachefiles/namei.c: remove duplicate header

linux/xattr.h is included more than once.

Link: http://lkml.kernel.org/r/5c86803d.1c69fb81.1a7c6.2b78@mx.google.com
Signed-off-by: Sabyasachi Gupta <sabyasachi.linux@gmail.com>
Acked-by: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>