Staging: hv: Rename struct storvsc_request_extension

Now that all duplicate state has been eliminated from
struct hv_storvsc_request and all needed state has been moved
to struct storvsc_request_extension, get rid of
struct hv_storvsc_request and rename struct storvsc_request_extension
as struct hv_storvsc_request. Cleanup and consolidation
of I/O request state is now complete.

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>