firmware: arm_scmi: Clean up a return statement in scmi_probe

The comments say "enabled" where "disabled" is intended.  Also it's
cleaner to return zero explicitly instead of ret.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/Y86im5M49p3ePGxj@kili


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>