fm10k: Corrected an error in Tx statistics

The function collecting Tx statistics was actually using values from the RX
ring. Thus, Tx and Rx statistics values reported by "ifconfig" will
return identical values. This change corrects this error and the Tx
statistics is now reading from the Tx ring.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Matthew Vick <matthew.vick@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>