net: fman: Remove some unused fields in some structure

In "struct muram_info", the 'size' field is unused.
In "struct memac_cfg", the 'fixed_link' field is unused.

Remove them.

Found with cppcheck, unusedStructMember.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/425222d4f6c584e8316ccb7b2ef415a85c96e455.1712084103.git.christophe.jaillet@wanadoo.fr


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