bcachefs: Fix pr_buf() calls

In a few places we were passing a variable to pr_buf() for the format
string - oops.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/opts.c

@@ -324,7 +324,7 @@ void bch2_opt_to_text(struct printbuf *out,
 		if (flags & OPT_SHOW_FULL_LIST)
 			bch2_string_opt_to_text(out, opt->choices, v);
 		else
-			pr_buf(out, opt->choices[v]);
+			pr_buf(out, "%s", opt->choices[v]);
 		break;
 	case BCH_OPT_FN:
 		opt->to_text(out, c, sb, v);

fs/bcachefs/util.h

@@ -388,7 +388,7 @@ static inline void pr_uuid(struct printbuf *out, u8 *uuid)
 	char uuid_str[40];
 
 	uuid_unparse_lower(uuid, uuid_str);
-	pr_buf(out, uuid_str);
+	pr_buf(out, "%s", uuid_str);
 }
 
 int bch2_strtoint_h(const char *, int *);