busdma: Fix powerpc DMA alignment check

The original logic was to check if there's no filter and the address is
misaligned relative to the requirements. The refactoring in
c606ab59e7f9423f7027320e9a4514c7db39658d missed this, and instead caused
it to return failure if the address *is* properly aligned.

(cherry picked from commit 3a9688f8bc488b16bf5676057fa86263554312b0)