xattr: remove redundant check on variable err

xattr: remove redundant check on variable err

Curretly in function generic_listxattr the for_each_xattr_handler loop
checks err and will return out of the function if err is non-zero.
It's impossible for err to be non-zero at the end of the function where
err is checked again for a non-zero value. The final non-zero check is
therefore redundant and can be removed. Also move the declaration of
err into the loop.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>