net: wan: framer: remove children from struct framer_ops kdoc

Remove documentation of non-existent children field
from the Kernel doc for struct framer_ops.

Introduced by 82c944d0 ("net: wan: Add framer framework support")

Signed-off-by: Simon Horman <horms@kernel.org>
Acked-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>