ARM: dts: msm: set maximum buffer length to solve malloc failure

Memory allocations of order of 4 and upwards are not
recommended by memory team. Fix a maximum buffer length of
32KB instead of the MHI supported maximum of 64KB.

Change-Id: I4527390463032223e941777fea7f48446555c029
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>