Staging: hv: netvsc_drv: Get rid of an unnecessary assignment in rndis_filter.c

Now that we compute the size of struct rndis_filter_packet where
it is needed, get rid of the unnecessary assignment.

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>