coresight: Cleanup coresight_remove_conns

When a device is unregistered, we remove all connection
references to it, by searching the connection records of
all devices in the coresight bus, via coresight_remove_conns.
We could avoid searching if this device doesn't have an input
port (e.g, a source). Also document the purpose of the function.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>