soc: qcom: pil-femto-modem: Flush cache before unmap

All memory write operations must be completed before passing
data size to mba.

Change-Id: I2f55faa7cf2c2cb8c69581d8d4011d8e813721d7
Acked-by: Kaushik Sikdar <ksikdar@qti.qualcomm.com>
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>