PCI/switchtec: Fix a MRPC error status handling issue

If an error is encountered when executing a MRPC command, the firmware
will set the status register to SWITCHTEC_MRPC_STATUS_ERROR and return
the error code in the return value register.

Add handling of SWITCHTEC_MRPC_STATUS_ERROR on status register when
completing a MRPC command.

Link: https://lore.kernel.org/r/20211014141859.11444-3-kelvin.cao@microchip.com
Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/switch/switchtec.c

@@ -238,7 +238,8 @@ static void mrpc_complete_cmd(struct switchtec_dev *stdev)
 	stuser_set_state(stuser, MRPC_DONE);
 	stuser->return_code = 0;
 
-	if (stuser->status != SWITCHTEC_MRPC_STATUS_DONE)
+	if (stuser->status != SWITCHTEC_MRPC_STATUS_DONE &&
+	    stuser->status != SWITCHTEC_MRPC_STATUS_ERROR)
 		goto out;
 
 	if (stdev->dma_mrpc)
@@ -622,7 +623,8 @@ static ssize_t switchtec_dev_read(struct file *filp, char __user *data,
 out:
 	mutex_unlock(&stdev->mrpc_mutex);
 
-	if (stuser->status == SWITCHTEC_MRPC_STATUS_DONE)
+	if (stuser->status == SWITCHTEC_MRPC_STATUS_DONE ||
+	    stuser->status == SWITCHTEC_MRPC_STATUS_ERROR)
 		return size;
 	else if (stuser->status == SWITCHTEC_MRPC_STATUS_INTERRUPTED)
 		return -ENXIO;