at91bootstrap: fix upstream URL

AT91Bootstrap 1.x seems to have disappeared from atmel.com (but return
HTML instead of a 404), so use the at91.com FTP server instead.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

boot/at91bootstrap/at91bootstrap.mk

@@ -4,7 +4,7 @@
 #
 #############################################################
 AT91BOOTSTRAP_VERSION = 1.16
-AT91BOOTSTRAP_SITE = http://www.atmel.com/Images
+AT91BOOTSTRAP_SITE = ftp://www.at91.com/pub/at91bootstrap/
 AT91BOOTSTRAP_SOURCE = AT91Bootstrap$(AT91BOOTSTRAP_VERSION).zip
 
 AT91BOOTSTRAP_BOARD = $(call qstrip,$(BR2_TARGET_AT91BOOTSTRAP_BOARD))