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@xxxxxxxxxxxx>