ARM: dts: msm: Remove DDR52 bus speed mode for sdm670

DDR52 mode puts the system in SVS power mode. This is breaking power
goals for certain video playbacks. So remove DDR52 so that the eMMC
driver will use HS50 mode instead. HS50 mode runs in low SVS.

Change-Id: I57abd272ea19dc82306a0516408f1a3a63a8f929
Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>