idpf: improve locking around idpf_vc_xn_push_free()

idpf: improve locking around idpf_vc_xn_push_free()

Protect the set_bit() operation for the free_xn bitmask in
idpf_vc_xn_push_free(), to make the locking consistent with rest of the
code and avoid potential races in that logic.

Fixes: 34c21fa894a1 ("idpf: implement virtchnl transaction manager")
Cc: stable@vger.kernel.org
Reported-by: Ray Zhang <sgzhang@google.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Samuel Salin <Samuel.salin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>