counter: microchip-tcb-capture: Add const qualifier for functions_list array

counter: microchip-tcb-capture: Add const qualifier for functions_list array

The struct counter_count functions_list member expects a const enum
counter_count_function array. This patch adds the const qualifier to the
mchp_tc_count_functions to match functions_list.

Cc: Kamel Bouhara <kamel.bouhara@bootlin.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/74cb91ab7b459563762ec28633cd8808093aa2ad.1623201081.git.vilhelm.gray@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>