libertas: allow for PS mode to be disabled when firmware doesn't support it

Otherwise, we go into an endless busy loop trying to enable PS mode when
the command queue is empty, dealing with the error response, and then
trying to enable PS mode again because the command queue is empty.... it
doesn't really save much power.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/libertas/dev.h b/drivers/net/wireless/libertas/dev.h
index fe50457..1c6ec4d 100644
--- a/drivers/net/wireless/libertas/dev.h
+++ b/drivers/net/wireless/libertas/dev.h
@@ -260,6 +260,7 @@
 	u16 psmode;		/* Wlan802_11PowermodeCAM=disable
 				   Wlan802_11PowermodeMAX_PSP=enable */
 	u32 psstate;
+	char ps_supported;
 	u8 needtowakeup;
 
 	struct PS_CMD_ConfirmSleep lbs_ps_confirm_sleep;