Read out error code when F/W returns STATUS_ERROR for MRPC command.
Read out error code when F/W returns STATUS_ERROR for MRPC command.

If an error is encountered when executing the MRPC command, firmware will set SWITCHTEC_MRPC_STATUS_ERROR and return the error code in 'return_value' register. We return this error code in 'errno'.

Microsemi/switchtec-user,Microsemi/switchtec-user