greybus: uart: Fix minor number leak

On the gb_uart_remove() path we are forgetting to do a release_minor()
leading to a minor number leak. This is a simple one-line fix.

Tested on EVT 2.0

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/uart.c

@@ -969,6 +969,7 @@ static void gb_uart_remove(struct gbphy_device *gbphy_dev)
 	gb_connection_disable(connection);
 	tty_port_destroy(&gb_tty->port);
 	gb_connection_destroy(connection);
+	release_minor(gb_tty);
 	kfifo_free(&gb_tty->write_fifo);
 	kfree(gb_tty->buffer);
 	kfree(gb_tty);