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>
diff --git a/include/configs/apx4devkit.h b/include/configs/apx4devkit.h
index 73c66af..ab4efa4 100644
--- a/include/configs/apx4devkit.h
+++ b/include/configs/apx4devkit.h
@@ -222,7 +222,7 @@
 		"root=ubi0:rootfs rootfstype=ubifs ${mtdparts} rw\0" \
 	"bootcmd_nand=" \
 		"run bootargs_nand && ubi part root 2048 && " \
-		"ubifsmount rootfs && ubifsload 41000000 boot/uImage && " \
+		"ubifsmount ubi:rootfs && ubifsload 41000000 boot/uImage && " \
 		"bootm 41000000\0" \
 	"bootargs_mmc=" \
 		"setenv bootargs ${kernelargs} " \