printf: Fix \c in %b in printf builtin exiting the shell after r337458

SVN r337458 erroneously partially reverted r265885.

This is immediately visible when running the Kyua/ATF tests for
usr.bin/printf, which actually test sh's printf builtin.

PR:		229641

usr.bin/printf/printf.c

@@ -388,7 +388,7 @@ printf_doformat(char *fmt, int *rval)
 
 		free(p);
 		if (getout)
-			exit(*rval);
+			return (end_fmt);
 		break;
 	}
 	case 'c': {