init/do_mounts.c: add maj:min syntax comment

The name_to_dev_t function has a comment block which lists the supported
syntaxes for the device name.  Add a bullet for the <major>:<minor>
syntax, which is already supported in the code

Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/do_mounts.c

@@ -197,6 +197,8 @@ done:
  *	   is a zero-filled hex representation of the 1-based partition number.
  *	7) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to
  *	   a partition with a known unique id.
+ *	8) <major>:<minor> major and minor number of the device separated by
+ *	   a colon.
  *
  *	If name doesn't have fall into the categories above, we return (0,0).
  *	block_class is used to check if something is a disk name. If the disk