drm/ttm/tests: Fix type conversion in ttm_pool_test

drm/ttm/tests: Fix type conversion in ttm_pool_test

Fix a warning about casting an integer of different size in
ttm_pool_alloc_basic_dma_addr() subtest. Cast the DMA address to
uintptr_t before casting it to a generic pointer.

Signed-off-by: Karolina Stolarek <karolina.stolarek@intel.com>
Cc: Christian König <christian.koenig@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202308150419.PaHfWntn-lkp@intel.com/
Link: https://patchwork.freedesktop.org/patch/msgid/20230816105508.1135410-1-karolina.stolarek@intel.com
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>