textsearch: fix Boyer-Moore text search bug

The current logic has a bug which cannot find matching pattern, if the
pattern is matched from the first character of target string.
for example:
	pattern=abc, string=abcdefg
	pattern=a,   string=abcdefg
Searching algorithm should return 0 for those things.
Signed-off-by: NJoonwoo Park <joonwpark81@gmail.com>
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

lib/ts_bm.c

@@ -63,7 +63,7 @@ static unsigned int bm_find(struct ts_config *conf, struct ts_state *state)
 	struct ts_bm *bm = ts_config_priv(conf);
 	unsigned int i, text_len, consumed = state->offset;
 	const u8 *text;
-	int shift = bm->patlen, bs;
+	int shift = bm->patlen - 1, bs;
 
 	for (;;) {
 		text_len = conf->get_next_block(consumed, &text, conf, state);