ARM: dts: msm: Increase rmtfs buffer size in 8917

The rmtfs buffer size requested by modem has been changed
1.5MB in 8917.
This results in a mismatch of requested buffer size
and allowable buffer size, thus causing an error and a
modem crash.

CRs-fixed: 1024120
Change-Id: I0d6a17e3a07532c4dabc6dd3bca7269bae0cb512
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>