staging: lustre: llite_lib.c Set ll_md_setattr function to be static

This fixes the following sparse warning:
llite_lib.c:1240:5: warning: symbol 'll_md_setattr' was not declared. Should it be static?

Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>