fm10k: fix mis-ordered parameters in declaration for .ndo_set_vf_bw

We've had support for setting both a minimum and maximum bandwidth via
.ndo_set_vf_bw since commit 883a9ccb ("fm10k: Add support for SR-IOV
to driver", 2014-09-20).

Likely because we do not support minimum rates, the declaration
mis-ordered the "unused" parameter, which causes warnings when analyzed
with cppcheck.

Fix this warning by properly declaring the min_rate and max_rate
variables in the declaration and definition (rather than using
"unused"). Also rename "rate" to max_rate so as to clarify that we only
support setting the maximum rate.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>