slimbus: qcom-ngd-ctrl: Constify static structs

slimbus: qcom-ngd-ctrl: Constify static structs

qcom_slim_qmi_msg_handlers[] and qcom_slim_ngd_qmi_svc_event_ops are
only used as input arguments to qmi_handle_init() which accepts const
pointers to both qmi_ops and qmi_msg_handler. Make them const to allow
the compiler to put them in read-only memory.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20201127102451.17114-6-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>