ixgbevf: Change ixgbe_read_reg to ixgbevf_read_reg

Change the ixgbe_read_reg function name to ixgbevf_read_reg to
avoid a namespace clash with the ixgbe driver. This will allow
ixgbe to take its register read function out-of-line to reduce
memory footprint.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>