msm: adsprpc: null pointer check for fl

Adding a null pointer check for fl before
dereferencing.

Change-Id: I384e9f3980cf8c42cb2eeb554cc3c1e38c3520c0
Acked-by: Krishnaiah Tadakamalla <ktadakam@qti.qualcomm.com>
Signed-off-by: Jeya R <jeyr@codeaurora.org>