common/cmd_pxe.c: Fix GCC 4.6 build warnings

Fix:
cmd_pxe.c: In function 'parse_pxefile_top':
cmd_pxe.c:941:5: warning: 'err' may be used uninitialized in this
  function [-Wuninitialized]
cmd_pxe.c:921:6: note: 'err' was declared here

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Jason Hobbs <jason.hobbs@calxeda.com>
Acked-by: Jason Hobbs <jason.hobbs@calxeda.com>

common/cmd_pxe.c

@@ -918,7 +918,7 @@ static int parse_menu(char **c, struct pxe_menu *cfg, char *b, int nest_level)
 {
 	struct token t;
 	char *s = *c;
-	int err;
+	int err = 0;
 
 	get_token(c, &t, L_KEYWORD);