common: image-fdt: correct fdt_blob for IMAGE_FORMAT_LEGACY

common: image-fdt: correct fdt_blob for IMAGE_FORMAT_LEGACY

If condition of "(load == image_start || load == image_data)" is true,
should use "fdt_addr = load;", but not "fdt_blob = (char *)image_data;",
or fdt_blob will be overridden by "fdt_blob = map_sysmem(fdt_addr, 0);"
at the end of the switch case.

Signed-off-by: Peng Fan <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Joe Hershberger <[email protected]>
Cc: Max Krummenacher <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Suriyan Ramasami <[email protected]>
Cc: Paul Kocialkowski <[email protected]>
Cc: Tom Rini <[email protected]>
Reviewed-by: Simon Glass <[email protected]>