slab: Adjust comment after refactoring of gfp.h

Reflect the change from the commit below.

Fixes: cb5a065b ("headers/deps: mm: Split <linux/gfp_types.h> out of <linux/gfp.h>")
Signed-off-by: Thorsten Scherer <t.scherer@eckelmann.de>
Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/slab.h

@@ -526,7 +526,7 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node) __assume_page_align
  * to be at least to the size.
  *
  * The @flags argument may be one of the GFP flags defined at
- * include/linux/gfp.h and described at
+ * include/linux/gfp_types.h and described at
  * :ref:`Documentation/core-api/mm-api.rst <mm-api-gfp-flags>`
  *
  * The recommended usage of the @flags is described at