kconfig: Fix warning "‘jump’ may be used uninitialized"

Warning:
In file included from scripts/kconfig/zconf.tab.c:2537:0:
scripts/kconfig/menu.c: In function ‘get_symbol_str’:
scripts/kconfig/menu.c:590:18: warning: ‘jump’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     jump->offset = strlen(r->s);

Simplifies the test logic because (head && local) means (jump != 0)
and makes GCC happy when checking if the jump pointer was initialized.
Signed-off-by: NPeter Kümmel <syntheticpp@gmx.net>
Signed-off-by: NMichal Marek <mmarek@suse.cz>
[ imported from Linux Kernel, commit 2d5603060967 ]
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>

scripts/kconfig/menu.c

@@ -548,7 +548,7 @@ static void get_prompt_str(struct gstr *r, struct property *prop,
 {
 	int i, j;
 	struct menu *submenu[8], *menu, *location = NULL;
-	struct jump_key *jump;
+	struct jump_key *jump = NULL;
 
 	str_printf(r, _("Prompt: %s\n"), _(prop->text));
 	menu = prop->menu->parent;
@@ -586,7 +586,7 @@ static void get_prompt_str(struct gstr *r, struct property *prop,
 		str_printf(r, _("  Location:\n"));
 		for (j = 4; --i >= 0; j += 2) {
 			menu = submenu[i];
-			if (head && location && menu == location)
+			if (jump && menu == location)
 				jump->offset = strlen(r->s);
 			str_printf(r, "%*c-> %s", j, ' ',
 				   _(menu_get_prompt(menu)));