tgsi/exec: Correctly reset NumOutputs before parsing the shader

tgsi/exec: Correctly reset NumOutputs before parsing the shader

Whenever we're binding the shaders we're incrementing NumOutputs,
assuming the parser spots an output decleration, but we were never
reseting the variable. That means that each subsequent bind of
a geometry shader would add its number of output to the number
of output bound by all previously ran shaders and our indexes
would get completely messed up.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: José Fonseca <jfonseca@vmware.com>