nvme: fix NULL derefence in nvme_ctrl_fast_io_fail_tmo_show/store

Adding entry for dev_attr_fast_io_fail_tmo to avoid the kernel crash
while reading and writing the fast_io_fail_tmo.

Fixes: 09fbed63 (nvme: export fast_io_fail_tmo to sysfs)
Signed-off-by: Gopal Tiwari <gtiwari@redhat.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -3379,6 +3379,8 @@ static umode_t nvme_dev_attrs_are_visible(struct kobject *kobj,
 		return 0;
 	if (a == &dev_attr_reconnect_delay.attr && !ctrl->opts)
 		return 0;
+	if (a == &dev_attr_fast_io_fail_tmo.attr && !ctrl->opts)
+		return 0;
 
 	return a->mode;
 }