fm10k: fix incorrect index calculation in fm10k_write_reta

The index calculated when looping through the indir array passed to
fm10k_write_reta was incorrectly calculated as the first part i needs to
be multiplied by 4.

Fixes: 0cfea7a65738 ("fm10k: fix possible null pointer deref after kcalloc", 2016-04-13)
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>