staging: unisys: visorbus: add error handling to boottotool_show

Don't just drop the error from visorchannel_read on the floor, report it.
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/visorbus/visorchipset.c

@@ -130,11 +130,16 @@ static ssize_t boottotool_show(struct device *dev,
 			       char *buf)
 {
 	struct efi_spar_indication efi_spar_indication;
+	int err;
 
-	visorchannel_read(chipset_dev->controlvm_channel,
-			  offsetof(struct spar_controlvm_channel_protocol,
-				   efi_spar_ind), &efi_spar_indication,
-			  sizeof(struct efi_spar_indication));
+	err = visorchannel_read(chipset_dev->controlvm_channel,
+				offsetof(struct spar_controlvm_channel_protocol,
+					 efi_spar_ind),
+				&efi_spar_indication,
+				sizeof(struct efi_spar_indication));
+
+	if (err)
+		return err;
 	return sprintf(buf, "%u\n", efi_spar_indication.boot_to_tool);
 }