Bluetooth: Don't force DISCOVERY_STOPPED state in inquiry_cache_flush

We are not supposed to force DISCOVERY_STOPPED in inquiry_cache_flush
because we may break the discovery state machine. For instance, during
interleaved discovery, when we are about to start inquiry, the state
machine forcibly goes to DISCOVERY_STOPPED while it should stay in
DISCOVERY_FINDING state.

This problem results in unexpected behaviors such as sending two
mgmt_discovering events to userspace (when only one event is expected)
and Stop Discovery failures.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>