fsl/fman: Remove comment referring to non-existent function

fm_set_max_frm() existed in the Freescale SDK as a callback for an
early_param. When this code was ported to the upstream kernel the
early_param was converted to a module_param making the reference to the
function incorrect. The rest of the comment already does a good job of
explaining the parameter so removing the reference to the non-existent
function seems like the best thing to do.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>