thunderbolt: Check return value of tb_sw_read() in usb4_switch_op()

The function misses checking return value of tb_sw_read() before it
accesses the value that was read. Fix this by checking the return value
first.

Fixes: b040798 ("thunderbolt: Add initial support for USB4")
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <yehezkelshb@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/usb4.c

@@ -182,6 +182,9 @@ static int usb4_switch_op(struct tb_switch *sw, u16 opcode, u8 *status)
 		return ret;
 
 	ret = tb_sw_read(sw, &val, TB_CFG_SWITCH, ROUTER_CS_26, 1);
+	if (ret)
+		return ret;
+
 	if (val & ROUTER_CS_26_ONS)
 		return -EOPNOTSUPP;