sdcard: am57xx-beagle-x15: u-boot.img has grown, use a count of 4 over 2

Reported-By: William A. Mills <wm.a.mills@gmail.com>
Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

tools/hwpack/am57xx-beagle-x15.conf

@@ -18,7 +18,7 @@ dd_spl_uboot_bs="128k"
 spl_name="MLO"
 
 uboot_name="u-boot.img"
-dd_uboot_count="2"
+dd_uboot_count="4"
 dd_uboot_seek="1"
 dd_uboot_conf=""
 dd_uboot_bs="384k"