init: reduce rootwait polling interval time to 5ms

For several devices, the rootwait time is sensitive because it directly
affects booting time.  The polling interval of rootwait is currently
100ms.  To save unnessesary waiting time, reduce the polling interval to
5 ms.

[akpm@linux-foundation.org: remove used-once #define]
Link: http://lkml.kernel.org/r/20161207060743.1728-1-js07.lee@samsung.comSigned-off-by: NJungseung Lee <js07.lee@samsung.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

init/do_mounts.c

@@ -588,7 +588,7 @@ void __init prepare_namespace(void)
 			saved_root_name);
 		while (driver_probe_done() != 0 ||
 			(ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
-			msleep(100);
+			msleep(5);
 		async_synchronize_full();
 	}