kernel: lantiq: ltq-vmmc: introduce user group for vmmc

asterisk-chan-lantiq is by now the only user of the VMMC interface.
And asterisk runs as user 'asterisk' which doesn't give it permission
to open the /dev/vmmc* devices.
Introduce a new user group 'vmmc' and give permission to access the
/dev/vmmc* devices to that group.
Another commit for asterisk-chan-lantiq will add the 'asterisk' user
to that group.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 37bbed6f95)

package/kernel/lantiq/ltq-vmmc/Makefile

@@ -29,6 +29,7 @@ define KernelPackage/ltq-vmmc
   DEPENDS:=@(TARGET_lantiq_xway||TARGET_lantiq_xrx200) +kmod-ltq-tapi
   FILES:=$(PKG_BUILD_DIR)/src/drv_vmmc.ko
   AUTOLOAD:=$(call AutoProbe,drv_vmmc)
+  USERID:=:vmmc=386
 endef
 
 define KernelPackage/ltq-vmmc/description

package/kernel/lantiq/ltq-vmmc/files/vmmc.init

@@ -8,6 +8,7 @@ start() {
 	for i in 10 11 12 13 14 15 16 17 18; do
 		if ! [ -e /dev/vmmc$i ]; then
 			mknod -m 664 /dev/vmmc$i c 122 $i
+			chown root:vmmc /dev/vmmc$i
 		fi
 	done
 }