mm: Removed @freeptr_offset to prevent doc warning

Removed @freeptr_offset to fix below doc warning.
./mm/slab_common.c:385: warning: Excess function parameter 'freeptr_offset' description in 'kmem_cache_create_usercopy'
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202408292249.5oUpnCbS-lkp@intel.com/Signed-off-by: R Sundar <prosunofficial@gmail.com>
Link: https://lore.kernel.org/r/20240902020555.11506-1-prosunofficial@gmail.comSigned-off-by: Christian Brauner <brauner@kernel.org>

mm/slab_common.c

@@ -341,7 +341,6 @@ do_kmem_cache_create_usercopy(const char *name,
  * for copying to userspace
  * @name: A string which is used in /proc/slabinfo to identify this cache.
  * @size: The size of objects to be created in this cache.
- * @freeptr_offset: Custom offset for the free pointer in RCU caches
  * @align: The required alignment for the objects.
  * @flags: SLAB flags
  * @useroffset: Usercopy region offset