net: NSH: fix kernel-doc notation warning

Use the struct member's name and the correct format to prevent a
kernel-doc warning.

nsh.h:200: warning: Function parameter or member 'context' not described in 'nsh_md1_ctx'

Fixes: 1f0b7744 ("net: add NSH header structures and helpers")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jiri Benc <jbenc@redhat.com>
Link: https://lore.kernel.org/r/20230714045127.18752-8-rdunlap@infradead.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>