kcm: only display blocked tooltip if device blocked

On a disabled "Connect" button in the device page of the bluedevil kcm, a helpful tooltip informs the user that they need to unblock the device to connect. This tooltip does not take into account that the button may be disabled for other reasons than the device being blocked, such as the device already being in the process of connecting, such as immediately after pressing the button. And in this case, the tooltip is just confusing, rather than helpful.

This change replaces the condition for displaying the tooltip, only showing it when the text actually applies, namely when the device is blocked.