Suppress unused warning when using shader_param
Suppress unused warning when using shader_param

Depending on what kind of parameters a shader_param struct contains, the
generated code may or may not use the i variable, leading to unused
warnings where shader_param is used.

The change made in this commit suppresses those warnings.

tempbottle/gfx,red75prime/gfx,davll/gfx,tanderegg/gfx,JohnColanduoni/gfx,Bastacyclop/gfx,tanderegg/gfx,sectopod/gfx-rs,aepsil0n/gfx-rs,ColinKinloch/gfx,gfx-rs/gfx-rs,ColinKinloch/gfx,alexcrichton/gfx,bvssvni/gfx-rs,mitchmindtree/gfx-rs,JohnColanduoni/gfx