msm: adsprpc: null pointer check for fl

Adding a null pointer check for fl before
dereferencing.

Change-Id: I1691a406f819d740b5649da40c41989c0943f9ce
Acked-by: Krishnaiah Tadakamalla <ktadakam@qti.qualcomm.com>
Signed-off-by: Jeya R <jeyr@codeaurora.org>