arm64: fix a warning and a typo in SWP emulation

The store-release-exclusive is missing the "L" that makes it a
release rather than a normal store-exclusive.

Remove a variable that is not used and causes a compiler warning.

Change-Id: I91633a352b805ed9af450b632c9ee394235637c4
Signed-off-by: Alex Van Brunt <avanbrunt@nvidia.com>
Reviewed-on: http://git-master/r/369076


Reviewed-by: Richard Wiley <rwiley@nvidia.com>
Reviewed-by: Automatic_Commit_Validation_User