lantiq: TDW89x0 - increase spi frequency

lantiq: TDW89x0 - increase spi frequency

Use the same max spi frequency as set in u-boot.

According to the datasheets, the Q64-104HIP as well as the Winbond
25Q64FVSIG support spi frequencies up to 50 MHz. During my tests, the
Q64-104HIP couldn't be recognized/initialized if the frequency
was > 40MHz.

Both chips do support fast read as well.

While touching the dts file, I fixed the dtc compiler warnings.

Signed-off-by: Mathias Kresin <openwrt@kresin.me>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47994 3c298f89-4303-0410-b956-a3cf2f4a3e73