remoteproc: Remove null character write of shared mem

remoteproc is writing '\0' in the shared mem region. This
region is shared among multiple clients that are also trying
to read. Hence they miss first character.

Remove this null character write, as this mem area is
supposed to be Read only.

Further during every subsystem reboot, this region is
initialized with default, hence no need to write this
region.

Signed-off-by: Jitendra Sharma <shajit@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
(cherry picked from commit 2d02d158)