[etherfabric] Avoid use of sleep() in driver code

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/etherfabric.c

 		 * because we want to use it, or because we're about
 		 * to reset the mac anyway
 		 */
-		sleep ( 2 );
+		mdelay ( 2000 );
 
 		if ( ! efab->link_up ) {
 			EFAB_ERR ( "!\n" );