Assigning the result of posix_acl_to_xattr() to an unsigned data type
(size/size_t) obscures possible errors.

Coverity CID: 1206.
Signed-off-by: NFlorin Malita <fmalita@gmail.com>
Acked-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>