staging: greybus: arche-apb-ctrl: declare struct of_device_id as const

Declare the 'arche_apb_ctrl_of_match' array as const. This array is only stored
in the .of_match_table field of a device_driver structure, which is declared as
const. This addresses the checkpatch warning:

WARNING: struct of_device_id should be normally const

Signed-off-by: Eva Rachel Retuya <eraretuya@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>