memory: mtk-smi: Use ARRAY_SIZE to define MTK_SMI_CLK_NR_MAX

This definition is tied to the number of SMI common clocks (the array
mtk_smi_common_clks): improve the definition by using the ARRAY_SIZE
macro instead. That will also reduce room for mistakes when updating
the aforementioned array in the future.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20211015151557.510726-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>