clk: samsung: Make of_device_id array const

Array of struct of_device_id may be be const as expected by
of_match_table field and of_find_matching_node_and_match() function.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>