mm/slab: fix kernel-doc func param names

Use corrected function parameter names to eliminate kernel-doc
warnings:

slab.h:142: warning: Function parameter or struct member 's' not described in 'slab_folio'
slab.h:142: warning: Excess function parameter 'slab' description in 'slab_folio'
slab.h:168: warning: Function parameter or struct member 's' not described in 'slab_page'
slab.h:168: warning: Excess function parameter 'slab' description in 'slab_page'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>