Bluetooth: BAP: Shell: BA fix add_pa_sync command

The command would attempt to parse the BASE and enter the
subgroup information in a NULL pointer.

The BASE copy was also done incorrectly, as it did not
properly take the UUID into account (which should be
moved to a helper function if we expect users to do this).

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>