CHROMIUM: WAR: misc: fastrpc: lock the send request

BUG=b:137202421
TEST=Run label_image in loop

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Abhinav Asati <asatiabhi@codeaurora.org>
(cherry picked from commit 578ccceae4a47e823992b4bda44c52448e8bd88f
https://github.com/ldts/qualcomm-lt-kernel/commits/chromiumos-4.14-iommu-mmap-gw-rebased-for-next

)
Change-Id: I8c5ffe3fbd8549690df173feed7f71535a28ba2c
Signed-off-by: Vamsi Singamsetty <vamssi@codeaurora.org>