Use a common method for updating mutable and immutable sampler
descriptors.

Bug: b/129523279
Test: dEQP-VK.texture.filtering.2d.formats.r8g8b8a8_unorm.*
Change-Id: I1ef82c8fe2cbb2e92f3dadce794346be525648b8
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29848
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>