wimax/i2400m: if a device reboot happens during probe, handle it

When a device reboot happens when we are under probe, with init_mutex
taken, make sure we can recover. Have dev_reset_handle set boot mode
and i2400m_msg_to_dev() will see it and fail gracefully instead of
timing out.

Found and diagnosed by Cindy H. Kao.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
diff --git a/drivers/net/wimax/i2400m/control.c b/drivers/net/wimax/i2400m/control.c
index d8e0cdf..f9399f2 100644
--- a/drivers/net/wimax/i2400m/control.c
+++ b/drivers/net/wimax/i2400m/control.c
@@ -695,6 +695,7 @@
 	d_fnstart(3, dev, "(i2400m %p buf %p len %zu)\n",
 		  i2400m, buf, buf_len);
 
+	rmb();		/* Make sure we see what i2400m_dev_reset_handle() */
 	if (i2400m->boot_mode)
 		return ERR_PTR(-ENODEV);