staging: wlags49_h2: Replace kmalloc+memset by kzalloc and add error handling.

Replace kmalloc+memset pair by kzalloc() in 'wl_wds_device_alloc()'.
Add error handling to avoid null derefernce.

Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>