uboot-phytec

cmd: adtimg: Rename internal symbols

With 'dtimg.c' renamed to 'adtimg.c', now ensure the naming
consistency in the internal implementation of 'adtimg.c'.

No functional change intended.

Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>