wlcore: sdio: check for valid platform device data before suspend

the wl pointer can be null In case only wlcore_sdio is probed while
no WiLink module is successfully probed, as in the case of mounting a
wl12xx module while using a device tree file configured with wl18xx
related settings.
In this case the system was crashing in wl1271_suspend() as platform
device data is not set.
Make sure wl the pointer is valid before using it.

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>