*: fix fallout from -Wunused-parameter

function                                             old     new   delta
bbunpack                                             358     366      +8
passwd_main                                         1070    1072      +2
handle_incoming_and_exit                            2651    2653      +2
getpty                                                88      86      -2
script_main                                          975     972      -3
inetd_main                                          2036    2033      -3
dname_enc                                            377     373      -4
make_new_session                                     474     462     -12
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/5 up/down: 12/-24)            Total: -12 bytes
   text    data     bss     dec     hex filename
 797429     658    7428  805515   c4a8b busybox_old
 797417     658    7428  805503   c4a7f busybox_unstripped

diff --git a/util-linux/fbset.c b/util-linux/fbset.c
index d616abd..ab7770d 100644
--- a/util-linux/fbset.c
+++ b/util-linux/fbset.c
@@ -170,10 +170,10 @@
 };
 #endif
 
+#if ENABLE_FEATURE_FBSET_READMODE
 static int readmode(struct fb_var_screeninfo *base, const char *fn,
 					const char *mode)
 {
-#if ENABLE_FEATURE_FBSET_READMODE
 	FILE *f;
 	char buf[256];
 	char *p = buf;
@@ -257,11 +257,9 @@
 				return 1;
 		}
 	}
-#else
-	bb_error_msg("mode reading not compiled in");
-#endif
 	return 0;
 }
+#endif
 
 static inline void setmode(struct fb_var_screeninfo *base,
 					struct fb_var_screeninfo *set)
@@ -389,9 +387,13 @@
 	fh = xopen(fbdev, O_RDONLY);
 	xioctl(fh, FBIOGET_VSCREENINFO, &var);
 	if (g_options & OPT_READMODE) {
+#if !ENABLE_FEATURE_FBSET_READMODE
+		bb_show_usage();
+#else
 		if (!readmode(&var, modefile, mode)) {
 			bb_error_msg_and_die("unknown video mode '%s'", mode);
 		}
+#endif
 	}
 
 	setmode(&var, &varset);