ARM: dts: msm: Vote for nominal bus frequencies for 8939

Currently USB driver is voting for maximum PCNOC frequency which
results in CX running at turbo and could cause thermal issues.
Hence vote for nominal bus frequencies for USB to DDR path
which help in avoiding thermal issues with USB connected and
also keeping USB performace numbers same as PNOC running at max
value.

CRs-Fixed: 722888
Change-Id: I791fc413c8de55844ac5dcf0ffb51ef891f52e86
Signed-off-by: Sujeet Kumar <ksujeet@codeaurora.org>