brcmsmac: Fix possible NULL pointer dereference in _dma_ctrlflags()

There's a debug message to warn if this function is passed a NULL
pointer, but in order to print the message we have to dereference the
pointer. Obviously this isn't a good idea, so remove the message.

Reported-by: Fengguang Wu <[e-mail]>
Signed-off-by: Seth Forshee <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

drivers/net/wireless/brcm80211/brcmsmac/dma.c

···
 {
 	uint dmactrlflags;
 
-	if (di == NULL) {
-		brcms_dbg_dma(di->core, "NULL dma handle\n");
+	if (di == NULL)
 		return 0;
-	}
 
 	dmactrlflags = di->dma.dmactrlflags;
 	dmactrlflags &= ~mask;