wined3d: Do not check the input signature element count for sm4+ shaders in shader_spirv_compile_arguments_init().

Shader model 4 fragment shaders can have more than 12 input varyings. That's
fine though, because we don't need to build a varying map for them in the
first place. Note that in principle the ERR in question could still be
triggered by e.g. attempting to use a shader model 4 fragment shader with a
shader model 3 vertex shader.