scatterlist: add missing function params to kernel-doc

Describe missing function parameters to prevent kernel-doc warnings:

lib/scatterlist.c:288: warning: Function parameter or member 'first_chunk' not described in '__sg_alloc_table'
lib/scatterlist.c:800: warning: Function parameter or member 'flags' not described in 'sg_miter_start'

Link: https://lkml.kernel.org/r/20230912060848.4673-1-rdunlap@infradead.org


Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>