Bluetooth: Fix not using log_strdup() for bt_uuid_str()

The string returned by bt_uuid_str() is not in ROM so log_strdup()
must be used on it. This also eliminates the following kind of warning
messages: "<err> log: argument 3 in log message "%s: start_handle
0x%04x end_handle 0x%04x type %s" missing log_strdup()."

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>