free(9) size for wi(4) @ USB

[Martin Pieuchot]

The driver already keeps track of the size of the allocated buffer, so
use it.

Diff is untested as I don't have a wi(4) @ USB.

ok?

Index: if_wi_usb.c
===================================================================
RCS file: /cvs/src/sys/dev/usb/if_wi_usb.c,v
retrieving revision 1.68
diff -u -p -r1.68 if_wi_usb.c
--- if_wi_usb.c 24 Nov 2015 17:11:40 -0000      1.68
+++ if_wi_usb.c 8 Nov 2018 16:53:12 -0000
@@ -409,9 +409,10 @@ wi_usb_detach(struct device *self, int f
 
        while (sc->wi_usb_nummem) {
                sc->wi_usb_nummem--;
-               if (sc->wi_usb_txmem[sc->wi_usb_nummem] != NULL)
-                       free(sc->wi_usb_txmem[sc->wi_usb_nummem], M_DEVBUF, 0);
+               free(sc->wi_usb_txmem[sc->wi_usb_nummem], M_DEVBUF,
+                 sc->wi_usb_txmemsize[sc->wi_usb_nummem]);
                sc->wi_usb_txmem[sc->wi_usb_nummem] = NULL;
+               sc->wi_usb_txmemsize[sc->wi_usb_nummem] = 0;
        }
 
        if (sc->wi_usb_ep[WI_USB_ENDPT_INTR] != NULL) {
@@ -541,8 +542,10 @@ wi_cmd_usb(struct wi_softc *wsc, int cmd
                /* free alloc_nicmem regions */
                while (sc->wi_usb_nummem) {
                        sc->wi_usb_nummem--;
-                       free(sc->wi_usb_txmem[sc->wi_usb_nummem], M_DEVBUF, 0);
+                       free(sc->wi_usb_txmem[sc->wi_usb_nummem], M_DEVBUF,
+                         sc->wi_usb_txmemsize[sc->wi_usb_nummem]);
                        sc->wi_usb_txmem[sc->wi_usb_nummem] = NULL;
+                       sc->wi_usb_txmemsize[sc->wi_usb_nummem] = 0;
                }
 
 #if 0