Bluetooth: host: Notify application about prepare write error

Notify application about prepare write error when continueing the write
procedure fails when RX thread is processing responses. It is possible
that this operation fails, either because of disconnection or ATT
timeout on the ATT bearer. Notify the application in case it needs to
clear up resources, e.g. the write parameters.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>