drm/amd/amdgpu/amdgpu_cs: Add a couple of missing function param descriptions

Fixes the following W=1 kernel build warning(s):

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c:685: warning: Function parameter or member 'backoff' not described in 'amdgpu_cs_parser_fini'
drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c:1655: warning: Function parameter or member 'map' not described in 'amdgpu_cs_find_mapping'

Cc: Alex Deucher <[e-mail]>
Cc: "Christian König" <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Sumit Semwal <[e-mail]>
Cc: Jerome Glisse <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

···
  * cs_parser_fini() - clean parser states
  * @parser:	parser structure holding parsing context.
  * @error:	error number
+ * @backoff:	indicator to backoff the reservation
  *
  * If error is set than unvalidate buffer, otherwise just free memory
  * used by parsing context.
···
  * @parser: command submission parser context
  * @addr: VM address
  * @bo: resulting BO of the mapping found
+ * @map: Placeholder to return found BO mapping
  *
  * Search the buffer objects in the command submission context for a certain
  * virtual memory address. Returns allocation structure when found, NULL