acpi_ec(4): Do not probe "successfully" if an error occurred

All of the 'goto out;' cases in this probe routine without explicit
initialization of 'ret' indicate error cases and were clearly intended
to use the initial definition of 'ret' with ENXIO. However, 'ret' was
accidentally squashed by reuse for a subroutine call near the beginning
of probe.

Use a different variable for the subroutine status to preserve ENXIO ret
for the 'goto out's as a minimal solution to the panic reported at attach
for now.

PR: 245757