Staging: hv: storvsc: Cleanup storvsc_device_alloc()

The code in storvsc_device_alloc() is not needed as this would be
done by default. Get rid of it. We still keep the function as we use
this hook to allocate per-LUN memory pools in a later patch.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>