libertas_tf: don't defer firmware loading until start()

Hello Lubomir Rintel,

This is a semi-automatic email about new static checker warnings.

The patch baa0280f08c7: "libertas_tf: don't defer firmware loading until start()" from Feb 20, 2019, leads to the following Smatch complaint:

drivers/net/wireless/marvell/libertas_tf/if_usb.c:256 if_usb_disconnect()
warn: variable dereferenced before check 'priv' (see line 254)

drivers/net/wireless/marvell/libertas_tf/if_usb.c
253

   254		if_usb_reset_device(priv);
                                    ^^^^^

The patch introduces a new dereference (inside the function).

255
256 if (priv)

                    ^^^^

Old code assumes "priv" could be NULL.

   257			lbtf_remove_card(priv);
   258	

regards,
dan carpenter