Revert "convert to zalloc"

This reverts commit 3414fd8df8.

src/drivers/bus/isa.c

 		      ioidx <= ISA_IOIDX_MAX ( driver ) ; ioidx++ ) {
 			/* Allocate struct isa_device */
 			if ( ! isa )
-				isa = zalloc ( sizeof ( *isa ) );
+				isa = malloc ( sizeof ( *isa ) );
 			if ( ! isa ) {
 				rc = -ENOMEM;
 				goto err;
 			}
+			memset ( isa, 0, sizeof ( *isa ) );
 			isa->driver = driver;
 			isa->ioaddr = ISA_IOADDR ( driver, ioidx );