tty: serial: msm: Make of_device_id array const

Make of_device_id array const, because all OF functions handle it as const.

Signed-off-by: Kiran Padwal <kiran.padwal@smartplayin.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>