rpi: always set fdt_addr to the correct value

rpi: always set fdt_addr to the correct value

The fdt_addr env have meaning only for the current runtime and it depends
on the dtb size or firmware version. If one save the environment to disk
and the loads it on the latter boot, the fdt_addr might change, what
result in passing incorrect dtb address to the kernel. Fix this by always
setting the fdt_addr env. This fixes system operation after saving the
env to disk and updating i.e. dtb files or firmware.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: I8f242e0d92ff7cc8557c0fd4a7459804270d5d6d