mesa: Returns correct error values from gl(Get)SamplerParameter*() in GLES3

Per GLES specification, the family of functions glGetSamplerParameter(iv/fv)
and glSamplerParameter(i/f/iv/fv) return an INVALID_OPERATION error if
sampler is not the name of a sampler object previously returned from a call
to GenSamplers.
In desktop GL, an GL_INVALID_VALUE is returned instead.

Fixes 6 dEQP failing tests:
* dEQP-GLES3.functional.negative_api.shader.get_sampler_parameteriv
* dEQP-GLES3.functional.negative_api.shader.get_sampler_parameterfv
* dEQP-GLES3.functional.negative_api.shader.sampler_parameteri
* dEQP-GLES3.functional.negative_api.shader.sampler_parameteriv
* dEQP-GLES3.functional.negative_api.shader.sampler_parameterf
* dEQP-GLES3.functional.negative_api.shader.sampler_parameterfv