panasonic-laptop: fix acpi_pcc_write_sset return value

In current implementation, acpi_pcc_write_sset return 1
if write is successful, 0 if write is failed.
But all the callers consider acpi_pcc_write_sset return 0
if write is successful and return negtive if write is failed.

This patch changes the implementation of acpi_pcc_write_sset to
return 0 if write is successful, -EIO if write is failed.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>