Code review comment for lp:~kdub/mir/mir-buffer-get-stride

The driver for the addition is https://code.launchpad.net/~kdub/mir/nested-buffer/+merge/303251, where we have a need to know the stride to implement mg::Buffer.

Stride could be hidden behind linear/software buffers only, but as things stand now, its a core buffer property thats used in different parts of the code.