mm: slab: fix comment for ARCH_KMALLOC_MINALIGN

The comment next to the ARCH_KMALLOC_MINALIGN definition says that
ARCH_KMALLOC_MINALIGN can be defined in arch headers. This is incorrect:
it's actually ARCH_DMA_MINALIGN that can be defined there.

Fix the comment.
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://lore.kernel.org/r/fe1ca7a25a054b61d1038686d07569416e287e7b.1651161548.git.andreyknvl@google.com

include/linux/slab.h

@@ -197,7 +197,7 @@ void kmem_dump_obj(void *object);
 /*
  * Some archs want to perform DMA into kmalloc caches and need a guaranteed
  * alignment larger than the alignment of a 64-bit integer.
- * Setting ARCH_KMALLOC_MINALIGN in arch headers allows that.
+ * Setting ARCH_DMA_MINALIGN in arch headers allows that.
  */
 #if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8
 #define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN