netfilter: xt_comment: drop unneeded unsigned qualifier

Since a string is stored, and not something like a MAC address that
would rely on (un)signedness, drop the qualifier.
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter/xt_comment.h

@@ -4,7 +4,7 @@
 #define XT_MAX_COMMENT_LEN 256
 
 struct xt_comment_info {
-	unsigned char comment[XT_MAX_COMMENT_LEN];
+	char comment[XT_MAX_COMMENT_LEN];
 };
 
 #endif /* XT_COMMENT_H */