ARM: dts: imx: ventana: remove container node from iomuxc nodes

The container node in the iomuxc node is no longer necessary and causes
pinctl errors on the Ventana boards with analog video capture
since aa12693e:

pinctrl core: initialized pinctrl subsystem
imx6q-pinctrl 20e0000.iomuxc: no groups defined in /soc/aips-bus@02000000/iomuxc@020e0000/adv7180grp
imx6q-pinctrl 20e0000.iomuxc: no groups defined in /soc/aips-bus@02000000/iomuxc@020e0000/ipu2_csi1grp
imx6q-pinctrl 20e0000.iomuxc: initialized IMX pinctrl driver
imx6q-pinctrl 20e0000.iomuxc: function 'iomuxc' not supported
imx6q-pinctrl 20e0000.iomuxc: invalid function iomuxc in map table
imx6q-pinctrl 20e0000.iomuxc: function 'iomuxc' not supported
imx6q-pinctrl 20e0000.iomuxc: invalid function iomuxc in map table

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>