ubifs: Allow ubifsmount volume reference by number

UBI can mount volumes by name or number  The current code forces you
to name the volume by prepending every name with "ubi:".

>From fs/ubifs/super.c
 * There are several ways to specify UBI volumes when mounting UBIFS:
 * o ubiX_Y    - UBI device number X, volume Y;
 * o ubiY      - UBI device number 0, volume Y;
 * o ubiX:NAME - mount UBI device X, volume with name NAME;
 * o ubi:NAME  - mount UBI device 0, volume with name NAME.

Now any name passed in any of the above forms are allowed.

Also update the configs that referenced ubifsmount.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>