Staging: hv: Get rid of request_ext_size from struct storvsc_driver_object

Now that struct storvsc_request_extension is part of struct hv_storvsc_request
get rid of the field request_ext_size from struct storvsc_driver_object.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>