OpenBSM: fix free() in au_read_rec error case

buf is a char ** and *buf is the allocated buffer.

PR:		267050
Reported by:	Robert Morris <rtm@lcs.mit.edu>
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation

contrib/openbsm/libbsm/bsm_io.c

@@ -4597,7 +4597,7 @@ au_read_rec(FILE *fp, u_char **buf)
 
 		if (fread(bptr, 1, ntohs(filenamelen), fp) <
 		    ntohs(filenamelen)) {
-			free(buf);
+			free(*buf);
 			errno = EINVAL;
 			return (-1);
 		}