Mark pw_error __dead in util.h

[Matthew Martin]

The function is already marked __dead in passwd.c, so appears to just be
an oversight.

diff --git util.h util.h
index dd64f478e23..752f8bb9fc5 100644
--- util.h
+++ util.h
@@ -97,7 +97,7 @@ void  pw_edit(int, const char *);
 void   pw_prompt(void);
 void   pw_copy(int, int, const struct passwd *, const struct passwd *);
 int    pw_scan(char *, struct passwd *, int *);
-void   pw_error(const char *, int, int);
+__dead void    pw_error(const char *, int, int);
 int    getptmfd(void);
 int    openpty(int *, int *, char *, const struct termios *,
            const struct winsize *);