GBE: initialize BTI structure to zero.
GBE: initialize BTI structure to zero.

Clear to zero to avoid garbage data, as we do not
assign it later for local/constant memory access.

v2:
  move initialization code into constructor.

Signed-off-by: Ruiling Song <286a174c1339c6eff91abc41c3a1012c95030c95@intel.com>
Reviewed-by: Yang Rong <78759e37dc7114caed18f74e7515c5cb519dbf6d@intel.com>

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