ARM: dts: Update Venus nominal and turbo freqs to 346Mhz and 520Mhz

Change the Venus clocks frequencies to keep in-line with the new clock
plan.

Change-Id: Iad70c4ff72e9ecbd5752acaefaf60b2f734d89bb
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>