Bluetooth: ISO: don't try to remove CIG if there are bound CIS left

Consider existing BOUND & CONNECT state CIS to block CIG removal.
Otherwise, under suitable timing conditions we may attempt to remove CIG
while Create CIS is pending, which fails.

Fixes: 26afbd82

 ("Bluetooth: Add initial implementation of CIS connections")
Signed-off-by: Pauli Virtanen <pav@iki.fi>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>