isl: Fix row pitch for linear buffers

isl: Fix row pitch for linear buffers

isl always aligned the row pitch to the surface's image alignment.  This
was sometimes wrong when the surface backed a VkBuffer. For a VkBuffer,
the surface's row pitch is set by VkBufferImageCopy::bufferRowLength,
whose required alignment is only that of the VkFormat.

In particular, VkBuffer rows are packed in many dEQP and Crucible tests.
And packed rows are rarely aligned to the surface's image alignment.

Fixes: dEQP-VK.pipeline.image.view_type.2d.format.r8g8b8a8_unorm.size.13x13