Release lower bus interface before passing removal IRP to PDO

Release lower bus interface before passing removal IRP to PDO

If the PDO is surprised removed then the FDO tries to retain its
reference to the PDO's bus interface byond its destruction. This will
cause an assertion failure in checked builds of XENBUS and may cause
memory corruption.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>