src/install: skip checksum verification for casync-based images
src/install: skip checksum verification for casync-based images

The checksum and size of casync 'images' as located in bundle is only
the checksum/size of the index file, not the size of the image itself.

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

jluebbe/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc