staging: lustre: llite: remove unused parameters from md_{get, set}xattr()

staging: lustre: llite: remove unused parameters from md_{get, set}xattr()

md_getxattr() and md_setxattr() each have several unused
parameters. Remove them and improve the naming or remaining
parameters.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-10792
Reviewed-on: https://review.whamcloud.com/
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>