nfp: make RTsym users handle absolute symbols correctly

Make the RTsym users access the size via the helper, which
takes care of special handling of absolute symbols.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Francois H. Theron <francois.theron@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>