kconfig: remove the rootmenu check in menu_add_prop()

This reverts commit ba6ff60d ("kconfig: don't emit warning upon
rootmenu's prompt redefinition").

At that time, rootmenu.prompt was always set first, then it was set
again if a "mainmenu" statement was specified in the Kconfig file.

This is no longer the case since commit 0724a7c3 ("kconfig: Don't
leak main menus during parsing"). Remove the unneeded check.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/menu.c

@@ -138,7 +138,7 @@ static struct property *menu_add_prop(enum prop_type type, char *prompt, struct
 			while (isspace(*prompt))
 				prompt++;
 		}
-		if (current_entry->prompt && current_entry != &rootmenu)
+		if (current_entry->prompt)
 			prop_warn(prop, "prompt redefined");
 
 		/* Apply all upper menus' visibilities to actual prompts. */