usb-gadget: fix warning in ethernet

Driver was taking max() of a size_t and u32 which causes complaint
about comparison of different types.

Stumbled on this accidently in my config, never used.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/usb/gadget/u_ether.c b/drivers/usb/gadget/u_ether.c
index 1eda968..2ac1d214 100644
--- a/drivers/usb/gadget/u_ether.c
+++ b/drivers/usb/gadget/u_ether.c
@@ -241,7 +241,7 @@
 	size -= size % out->maxpacket;
 
 	if (dev->port_usb->is_fixed)
-		size = max(size, dev->port_usb->fixed_out_len);
+		size = max_t(size_t, size, dev->port_usb->fixed_out_len);
 
 	skb = alloc_skb(size + NET_IP_ALIGN, gfp_flags);
 	if (skb == NULL) {