ARM: dts: msm: Add maximum bus vote for SDM450

SDM450 target is missing maximum bus vote for XO
power level and hence adding it.

If max bus vote is not defined then bus vote for
that power level will be same as default and defeat
the purpose of having min, max and default voting
at any level.

Change-Id: Ib563133775bbe191d54cf5d4dcb75a60457614a8
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>