pinctrl: mediatek: Initialize variable *buf to zero

pinctrl: mediatek: Initialize variable *buf to zero

Coverity spotted that *buf is not initialized to zero in
mtk_pctrl_dbg_show. Using uninitialized variable *buf as argument to %s
when calling seq_printf. Fix this coverity by initializing *buf as zero.

Fixes: 184d8e13f9b1 ("pinctrl: mediatek: Add support for pin configuration dump via debugfs.")
Signed-off-by: Guodong Liu <Guodong.Liu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230118062036.26258-3-Guodong.Liu@mediatek.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>