fdt: Swap the signature for board_fdt_blob_setup()

fdt: Swap the signature for board_fdt_blob_setup()

This returns a devicetree and updates a parameter with an error code.
Swap it, since this fits better with the way U-Boot normally works. It
also (more easily) allows leaving the existing pointer unchanged.

No yaks were harmed in this change, but there is a very small code-size
reduction.

For sifive, the OF_BOARD option must be set for the function to be
called, so there is no point in checking it again. Also OF_SEPARATE is
defined always.

Signed-off-by: Simon Glass <[email protected]>
Reviewed-by: Matthias Brugger <[email protected]>
Reviewed-by: Patrice Chotard <[email protected]>
[trini: Update total_compute]
Signed-off-by: Tom Rini <[email protected]>