msm: adsprpc: Fix double fetch from fastrpc HLOS driver

Fix possible Buffer overflow due to double fetch from
fastrpc HLOS driver.

Change-Id: I03cf94e7f6fef9c8765404a6da3da47fe3bedf8b
Acked-by: Deepika Singh <dsi@qti.qualcomm.com>
Signed-off-by: Jeya R <jeyr@codeaurora.org>