zink: Add missing Flat decorations on some inputs.

zink: Add missing Flat decorations on some inputs.

Fixes validation failures:

Test case 'dEQP-GLES31.functional.android_extension_pack.shaders.es32.extension_directive.oes_sample_variables'..
MESA: error: Validation Error: [
UNASSIGNED-CoreValidation-Shader-InconsistentSpirv ] Object 0: handle =
0x563a1838b790, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x6bbb14 |
SPIR-V module not valid: [VUID-StandaloneSpirv-Flat-04744] Fragment
OpEntryPoint operand 31 with Input interfaces with integer or float type
must have a Flat decoration for Entry Point id 4.
%gl_SampleId = OpVariable %_ptr_Input_uint Input

Test case 'KHR-GL46.shader_ballot_tests.ShaderBallotAvailability'..
MESA: error: Validation Error: [ UNASSIGNED-CoreValidation-Shader-InconsistentSpirv ] Object 0: handle = 0x5558e12f17e0, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x6bbb14 | SPIR-V module not valid: [VUID-StandaloneSpirv-Flat-04744] Fragment OpEntryPoint operand 28 with Input interfaces with integer or float type must have a Flat decoration for Entry Point id 4.
  %gl_SubgroupLocalInvocationId = OpVariable %_ptr_Input_uint Input

Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20756>