Block members were getting decorations applied from all previous
block members. For example, in this case:
in InterfaceBlock {
 layout(location = 0) in vec4 in_color_smooth;
 layout(location = 1) in flat vec4 in_color_flat;
 layout(location = 2) in noperspective vec4 in_color_noperspective;
 layout(location = 3) in centroid vec4 in_color_centroid;
}

- the member at location 2 would get decorated with both flat and
  noperspective
- the member at location 3 would get decorated with both flat,
  noperspective and centroid

I added a local variable for the member decorations in order to not
bleed information between block members.

Bug: b/163600604
Change-Id: I6b79609f19ae2f2f48909af929f798a48b4cde34
Tests: dEQP-VK.draw.multiple_interpolation.structured.*
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47649
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>