Correct locking annotation for p_comm.

p_comm is changed during exec, it is not read-only after fork.

Pointed out by:	rwatson
Approved by:	re (gjb, kib)
MFC after:	1 week

sys/sys/proc.h

@@ -602,7 +602,7 @@ struct proc {
 	u_int		p_magic;	/* (b) Magic number. */
 	int		p_osrel;	/* (x) osreldate for the
 					       binary (from ELF note, if any) */
-	char		p_comm[MAXCOMLEN + 1];	/* (b) Process name. */
+	char		p_comm[MAXCOMLEN + 1];	/* (x) Process name. */
 	struct sysentvec *p_sysent;	/* (b) Syscall dispatch info. */
 	struct pargs	*p_args;	/* (c) Process arguments. */
 	rlim_t		p_cpulimit;	/* (c) Current CPU limit in seconds. */