mt76: backport rx buffer allocation fix from r46409

package/kernel/mt76/patches/100-dma-fix-rx-buffer-allocation-size.patch

+From: Felix Fietkau <nbd@openwrt.org>
+Date: Sat, 18 Jul 2015 17:51:24 +0200
+Subject: [PATCH] dma: fix rx buffer allocation size
+
+Signed-off-by: Felix Fietkau <nbd@openwrt.org>
+---
+
+--- a/dma.c
++++ b/dma.c
+@@ -158,7 +158,7 @@ mt76_dma_rx_fill(struct mt76_dev *dev, s
+ 	while (q->queued < q->ndesc - 1) {
+ 		int offset = mt76_rx_buf_offset(dev);
+ 
+-		buf = kzalloc(len, GFP_ATOMIC);
++		buf = kzalloc(q->buf_size, GFP_ATOMIC);
+ 		if (!buf)
+ 			break;
+