drivers:misc: ti-st: fix unexpected UART close

If suppose the UIM were to die and hence UART were to close when the
Bluetooth/FM or GPS is turned on, prep the ST for a state where-in if
the UIM comes back up, Bluetooth/FM/GPS can be turned on.

Signed-off-by: Pavan Savoy <pavan_savoy@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>