x86: Make do_zboot_states() static

This function is only called within zboot.c so make the function
private.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/x86/zboot.c b/cmd/x86/zboot.c
index 94e602b8..3035172 100644
--- a/cmd/x86/zboot.c
+++ b/cmd/x86/zboot.c
@@ -119,8 +119,8 @@
 	U_BOOT_CMD_MKENT(dump, 2, 1, do_zboot_dump, "", ""),
 )
 
-int do_zboot_states(struct cmd_tbl *cmdtp, int flag, int argc,
-		    char *const argv[], int state_mask)
+static int do_zboot_states(struct cmd_tbl *cmdtp, int flag, int argc,
+			   char *const argv[], int state_mask)
 {
 	int ret = 0;