b43: fix a lower bounds test

The problem is that "channel" is an unsigned int, when it's less 5 the
value of "channel - 5" is not a negative number as one would expect but
is very high positive value instead.

This means that "start" becomes a very high positive value.  The result
of that is that we never enter the "for (i = start; i <= end; i++) {"
loop.  Instead of storing the result from b43legacy_radio_aci_detect()
it just uses zero.

Fixes: ef1a628d ("b43: Implement dynamic PHY API")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Michael Büsch <m@bues.ch>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211006073621.GE8404@kili

drivers/net/wireless/broadcom/b43/phy_g.c

@@ -2297,7 +2297,7 @@ static u8 b43_gphy_aci_scan(struct b43_wldev *dev)
 	b43_phy_mask(dev, B43_PHY_G_CRS, 0x7FFF);
 	b43_set_all_gains(dev, 3, 8, 1);
 
-	start = (channel - 5 > 0) ? channel - 5 : 1;
+	start = (channel > 5) ? channel - 5 : 1;
 	end = (channel + 5 < 14) ? channel + 5 : 13;
 
 	for (i = start; i <= end; i++) {