acpi/nfit: fix cmd_rc for acpi_nfit_ctl to always return a value

cmd_rc is passed in by reference to the acpi_nfit_ctl() function and the
caller expects a value returned. However, when the package is pass through
via the ND_CMD_CALL command, cmd_rc is not touched. Make sure cmd_rc is
always set.

Fixes: aef25338 ("libnvdimm, nfit: centralize command status translation")

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>