input: synaptics_dsx: reallocate buffer under lock.

Prevent concurrent usage & re-allocation of the wr_buf variable.
Based off patch by chengengjia <chengjia4574@gmail.com>.

Change-Id: I88d78e1ec0fc9e88b1e6824c06161b67d01136ec
Signed-off-by: Andrew Chant <achant@google.com>
Git-commit: d740e7228bd1578ed01762998b2a86e7df56e608
Git-repo: https://android.googlesource.com/kernel/msm


Signed-off-by: Dennis Cagle <d-cagle@codeaurora.org>
Signed-off-by: Venkata Prahlad Valluru <vvalluru@codeaurora.org>