dt-bindings: mailbox: Update maintainer email for qcom apcs-kpss

Sivaprakash's codeaurora.org email address bounces.  Before he comes
back with his new email, fill Jassi's address in there.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>