lantiq: VGV7510KW22/VGV7519 update spi pinmux group

lantiq: VGV7510KW22/VGV7519 update spi pinmux group

With the backport of the kernel 4.5 pinctrl-xway patches (3551609d &
826bca29) the pinmux group "spi" was splitted into "spi_di", "spi_do" &
"spi_clk". But the no longer existing group "spi" is still used by some
device tree source files.

This fixes the detection of the wireless chipset of the VGV7510KW22.

Signed-off-by: Mathias Kresin <openwrt@kresin.me>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48658 3c298f89-4303-0410-b956-a3cf2f4a3e73