[vulkan] Set min_buffer_count

Currently we set min_buffer_count_for_camping, which doesn't make sense
(since it's the application that decides how the buffers are used,
not the driver). min_buffer_count, which was recently added, makes more
sense.

Change-Id: I480ff5a6987cb14017c1b15012687f52d6ec9507
1 file changed