common/image.c: Fix regression with ramdisk load/entry points in FIT

A FIT image with a ramdisk that sets the entry or load points to 0x0
must be treated as meaning "leave in place" and NOT "relocate to 0x0".
This regression was introduced in a51ec63b.

Signed-off-by: Stefano Babic <sbabic@denx.de>