thunderbolt: Fail switch adding operation if reading DROM fails

All non-root switches are expected to have DROM so if the operation
fails, it might be due the user unlugging the device. There is no point
continuing adding the switch further in that case. Just bail out.

For root switches (hosts) the DROM is either retrieved from a EFI
variable, NVM or hard-coded.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Michael Jamet <michael.jamet@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>