drm/xe/psmi: Do not return NULL

The checks for id and bo_size are impossible conditions. If they were
possible, then the caller should not be using IS_ERR(). Just replace
them with asserts which should be compiled out when not debugging and
at the same time prevent other refactors to break this assumption.

Reported-by: Dan Carpenter <[e-mail]>
Closes: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Rodrigo Vivi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/xe_psmi.c

···
 {
 	struct xe_tile *tile;
 
-	if (!id || !bo_size)
-		return NULL;
+	xe_assert(xe, id);
+	xe_assert(xe, bo_size);
 
 	tile = &xe->tiles[id - 1];