mod/xr77128: Extend get_dev_ctx to support sub-element IDs
Previously, get_dev_ctx was restricted to accepting only element IDs due to an assert check. However, in release builds, it functions correctly with both element and sub-element IDs.
This change updates the assert to explicitly allow sub-element IDs as well.
Signed-off-by: Mohamed Omar Asaker mohamed.omarasaker@arm.com