memory: mtk-smi: handle positive return value for clk_bulk_prepare_enable

Function clk_bulk_prepare_enable() returns 0 for success or a negative
number for error, although the common style for the callers is to check
always for any non-zero return value (just like its implementation in
clk.h does).  Adjust the code to such coding style.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220113111057.29918-6-yong.wu@mediatek.com


[krzysztof: rewrite commit msg]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>