util: Fix warning with const qualifier from bsearch

  CC       src/util.o
src/util.c: In function ‘codepoint_lookup’:
src/util.c:2643:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
 2643 |         result = bsearch(key, table, len, sizeof(struct codepoint),
      |                ^

src/util.c

diff --git a/src/util.c b/src/util.c
index bfe46ef..b6a9bb4 100644
--- a/src/util.c
+++ b/src/util.c
@@ -2638,7 +2638,7 @@
 					const struct codepoint *table,
 					unsigned int len)
 {
-	struct codepoint *result = NULL;
+	const struct codepoint *result;
 
 	result = bsearch(key, table, len, sizeof(struct codepoint),
 				compare_codepoints);