beep: disallow FEATURE_BEEP_FREQ = 0 in configuration

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/miscutils/beep.c b/miscutils/beep.c
index 14802b5..216f694 100644
--- a/miscutils/beep.c
+++ b/miscutils/beep.c
@@ -16,7 +16,7 @@
 //config:
 //config:config FEATURE_BEEP_FREQ
 //config:	int "default frequency"
-//config:	range 0 2147483647
+//config:	range 20 50000	# allowing 0 here breaks the build
 //config:	default 4000
 //config:	depends on BEEP
 //config:	help