imx: hab: Allow hab_auth_img_or_fail to be called without ivt_offset

imx: hab: Allow hab_auth_img_or_fail to be called without ivt_offset

Since commit ea91031b2232 ("imx: hab: extend hab_auth_img to calculate
ivt_offset"), it is possible to call the hab_auth_img command without the
last ivt_offset argument.

Currently, calling hab_auth_img_or_fail without the last
ivt_offset parameter causes a failure and the command usage text is shown.

Fix this problem by adjusting the argc logic to allow
calling hab_auth_img_or_fail with only the address and size parameters.

This way, both hab_auth_img and hab_auth_img_or_fail have the same
behavior with respect to the allowed number of command parameters.

Signed-off-by: Eduard Strehlau <eduard@lionizers.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>