Rename ttm_bo_init to ttm_bo_init_validate since that better matches
what the function is actually doing.

Remove the unused size parameter, move the function's kerneldoc to the
implementation and cleanup the whole error handling.
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220707102453.3633-2-christian.koenig@amd.comReviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>