mm: Removed @freeptr_offset to prevent doc warning

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.com
Signed-off-by: Christian Brauner <brauner@kernel.org>