drm/ttm: fix logic inversion in ttm_eu_reserve_buffers

That should have been max, not min.

Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: c8d4c18b

 ("dma-buf/drivers: make reserving a shared slot mandatory v4")
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220411134537.2854-1-christian.koenig@amd.com