Staging: sxg: Fix memory leak caused by double allocation of rings

* The receive rings were getting allocated twice. Once at probe time
  and once at open time. This leaked huge amounts of memory.
  Fix this leak and now allocation is done only once.

Signed-off-by: LinSysSoft Sahara Team <saharaproj@linsyssoft.com>
Signed-off-by: Mithlesh Thukral <mithlesh@linsyssoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>