update boot.wim path

boot.wim is generally located in the sources directory of the image. The "echo" showed the correct path, but the initrd command attempted to load from the wrong path.

roles/netbootxyz/templates/menu/windows.ipxe.j2

@@ -48,7 +48,7 @@ initrd -n bootmgr     ${win_base_url}/${win_arch}/bootmgr       bootmgr ||
 initrd -n bootmgr.efi ${win_base_url}/${win_arch}/bootmgr.efi   bootmgr.efi ||      
 initrd -n bcd         ${win_base_url}/${win_arch}/boot/bcd      bcd
 initrd -n boot.sdi    ${win_base_url}/${win_arch}/boot/boot.sdi boot.sdi   
-initrd -n boot.wim    ${win_base_url}/${win_arch}/boot/boot.wim boot.wim
+initrd -n boot.wim    ${win_base_url}/${win_arch}/sources/boot.wim boot.wim
 boot
 
 :windows_exit