hidhost: Don't attempt to reconnect hidhost

The upper layer may call bthh_interface_t->connect when HidHost is
already connected for that remote device. In that case, we should not
attempt to connect again to prevent btif_hh_cb.status from being stuck
at CONNECTING, which will cause subsequent HidHost connects to always
fail.

Bug: 216352373
Tag: #floss
Test: Chrome OS bluetooth_AdapterMDHealth.md_two_connections_test.floss

Change-Id: Ie822fc44d70194cd91557794e0c65dc679b871c9