b43: Add slot count compiletime assertion

This adds a compiletime assertion for a recently introduced
assumption on the slot counts.
The tx header cache handling code assumes that the TX slot count
can be divided evenly by the number of TX slots per frame.
Signed-off-by: NMichael Buesch <mb@bu3sch.de>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/dma.c

@@ -842,6 +842,9 @@ struct b43_dmaring *b43_setup_dmaring(struct b43_wldev *dev,
 #endif
 
 	if (for_tx) {
+		/* Assumption: B43_TXRING_SLOTS can be divided by TX_SLOTS_PER_FRAME */
+		BUILD_BUG_ON(B43_TXRING_SLOTS % TX_SLOTS_PER_FRAME != 0);
+
 		ring->txhdr_cache = kcalloc(ring->nr_slots / TX_SLOTS_PER_FRAME,
 					    b43_txhdr_size(dev),
 					    GFP_KERNEL);