The imageView's baseMipLevel is already taken into account when
obtaining each level's parameters, so don't offset a second time.

Bug b/129523279
Tests: dEQP-VK.texture.mipmap.*
Change-Id: I5a5c35f36d2f8517136c095f8c80202984a777bd
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31690
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>