msm: adsprpc: Check size with length passed by client

Check whether size of fd is greater than or equal to
length passed by client. If its not checked here, client
might access unmapped address on dsp.

Change-Id: I4e176f32b0f263e2f7bf648e03b4ca904479527b
Acked-by: Deepika Singh <dsi@qti.qualcomm.com>
Signed-off-by: Mohammed Nayeem Ur Rahman <mohara@codeaurora.org>