Staging: hv: storvsc: Fix a bug in copy_from_bounce_buffer()

Fix a bug in copy_from_bounce_buffer().

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>