ARM: dts: msm: Increase rmtfs buffer size in 8940

The rmtfs buffer size requested by modem has been changed
1.5MB in 8940.
This results in a mismatch of requested buffer size
and allowable buffer size, thus causing an error and a
modem crash.

CRs-fixed: 1017343
Change-Id: I44a127abc216a9ee6fdd8c734d988247d75766cb
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>