locking/atomic: scripts: remove bogus order parameter

At the start of gen_proto_order_variants(), the ${order} variable is not
yet defined, and will be substituted with an empty string.

Replace the current bogus use of ${order} with an empty string instead.

This results in no change to the generated headers.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230605070124.3741859-15-mark.rutland@arm.com