USB: build fix

this config:

http://redhat.com/~mingo/misc/config-Wed_Apr_30_15_12_48_CEST_2008.bad

fails to build due to an #error. Turn that into a #warning instead
to not break randconfig builds unnecessarily.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/net/usb/cdc_subset.c

@@ -218,7 +218,7 @@ static const struct driver_info	blob_info = {
 /*-------------------------------------------------------------------------*/
 
 #ifndef	HAVE_HARDWARE
-#error You need to configure some hardware for this driver
+#warning You need to configure some hardware for this driver
 #endif
 
 /*