prism54: off by one BUG_ON() test

This code was supposed to trigger a BUG() if we truncate the output but
it's off by one so it allows one character to be truncated.  Really
drivers shouldn't call BUG_ON() and especially for something minor like
this so I've changed it to a WARN_ON().
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/intersil/prism54/isl_ioctl.c

@@ -2036,7 +2036,7 @@ format_event(islpci_private *priv, char *dest, const char *str,
 			 mlme->address,
 			 (error ? (mlme->code ? " : REJECTED " : " : ACCEPTED ")
 			  : ""), mlme->code);
-	BUG_ON(n > IW_CUSTOM_MAX);
+	WARN_ON(n >= IW_CUSTOM_MAX);
 	*length = n;
 }