Staging: hv: Move the context field from struct hv_storvsc_request

Staging: hv: Move the context field from struct hv_storvsc_request

In preparation of consolidating all I/O request state, move
the context field from struct hv_storvsc_request to
struct storvsc_request_extension.

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>