staging: brcm80211: restrict MIPS dma bug workaround to BCM47XX

The inline function dma_spin_for_len() was defined for MIPS platforms
but the problem only occurs with dma of the PCI core in bcm47xx chips.
This patch restricts the function further to BCM47XX platforms only.

Tested on BCM63281.
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Tested-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/brcm80211/brcmsmac/dma.h

@@ -100,21 +100,21 @@ void dma_walk_packets(struct dma_pub *dmah, void (*callback_fnc)
 		      (void *pkt, void *arg_a), void *arg_a);
 
 /*
- * DMA(Bug) on some chips seems to declare that the packet is ready, but the
- * packet length is not updated yet (by DMA) on the expected time.
+ * DMA(Bug) on bcm47xx chips seems to declare that the packet is ready, but
+ * the packet length is not updated yet (by DMA) on the expected time.
  * Workaround is to hold processor till DMA updates the length, and stay off
  * the bus to allow DMA update the length in buffer
  */
 static inline void dma_spin_for_len(uint len, struct sk_buff *head)
 {
-#if defined(__mips__)
+#if defined(CONFIG_BCM47XX)
 	if (!len) {
 		while (!(len = *(u16 *) KSEG1ADDR(head->data)))
 			udelay(1);
 
 		*(u16 *) (head->data) = cpu_to_le16((u16) len);
 	}
-#endif				/* defined(__mips__) */
+#endif				/* defined(CONFIG_BCM47XX) */
 }
 
 #endif				/* _BRCM_DMA_H_ */