net: wireless: b43legacy: Replace GFP_ATOMIC with GFP_KERNEL in dma_tx_fragment

dma_tx_fragment() is never called in atomic context.

dma_tx_fragment() is only called by b43legacy_dma_tx(), which is
only called by b43legacy_tx_work().
b43legacy_tx_work() is only set a parameter of INIT_WORK() in
b43legacy_wireless_init().

Despite never getting called from atomic context,
dma_tx_fragment() calls alloc_skb() with GFP_ATOMIC,
which does not sleep for allocation.
GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL,
which can sleep and improve the possibility of sucessful allocation.

This is found by a static analysis tool named DCNS written by myself.
And I also manually check it.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/broadcom/b43legacy/dma.c

@@ -1064,7 +1064,7 @@ static int dma_tx_fragment(struct b43legacy_dmaring *ring,
 	meta->dmaaddr = map_descbuffer(ring, skb->data, skb->len, 1);
 	/* create a bounce buffer in zone_dma on mapping failure. */
 	if (b43legacy_dma_mapping_error(ring, meta->dmaaddr, skb->len, 1)) {
-		bounce_skb = alloc_skb(skb->len, GFP_ATOMIC | GFP_DMA);
+		bounce_skb = alloc_skb(skb->len, GFP_KERNEL | GFP_DMA);
 		if (!bounce_skb) {
 			ring->current_slot = old_top_slot;
 			ring->used_slots = old_used_slots;