net: brcm80211: fix range check

Unsigned minus constant is still unsigned so checking its sign makes no
sense.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -4585,7 +4585,7 @@ static int brcms_b_attach(struct brcms_c_info *wlc, struct bcma_device *core,
 		wlc_hw->machwcap_backup = wlc_hw->machwcap;
 
 		/* init tx fifo size */
-		WARN_ON((wlc_hw->corerev - XMTFIFOTBL_STARTREV) < 0 ||
+		WARN_ON(wlc_hw->corerev < XMTFIFOTBL_STARTREV ||
 			(wlc_hw->corerev - XMTFIFOTBL_STARTREV) >
 				ARRAY_SIZE(xmtfifo_sz));
 		wlc_hw->xmtfifo_sz =