fsi: sbefifo: Add missing mutex_unlock

There was no unlock of the FFDC mutex.

Fixes: 9f4a8a2d7f9d ("fsi/sbefifo: Add driver for the SBE FIFO")
Signed-off-by: Eddie James <eajames@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/fsi/fsi-sbefifo.c

@@ -194,6 +194,7 @@ static void sbefifo_dump_ffdc(struct device *dev, const __be32 *ffdc,
 		}
 		dev_warn(dev, "+-------------------------------------------+\n");
 	}
+	mutex_unlock(&sbefifo_ffdc_mutex);
 }
 
 int sbefifo_parse_status(struct device *dev, u16 cmd, __be32 *response,