s5p-fimc: Don't allow application to choose the buffer size

This is not allowed by the spec, and only served the purpose of hiding bugs
in size calculation so far.
Merge pull request #1 from ndufresne/endless

Endless: FIMC driver misc fixes
Revert "s5p-fimc: Don't allow application to choose the buffer size"

This reverts commit c4c988939370b677a18c2346ed9ae25cc361e02d.
The line of code added here is bad, and results in error:
    dma_alloc_coherent of size 0 failed
s5p-fimc: Use roundup() instead of ALIGN()

The size of a row is not always a power of two, so ALIGN cannot be used.