SystemUI: Check whether the selected WFD route is available

When the selected WFD route is not available, the cast tile in
quick settings and the cast slot in the status bar are both shown
as a connected icon, it is not reasonable. This CL checks whether
the selected route is available when getting the cast devices.

Bug: 247925238
Test: Mannual
Change-Id: Ifdbf4c61e95504ae7fc24933695e6fd348d75750