i40e: Simplify the do-while allocation loop

Fold the count decrement into the while-statement.
Reviewed-by: NMaciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: NBjörn Töpel <bjorn.topel@intel.com>
Tested-by: NKiran Bhandare <kiranx.bhandare@intel.com>
Signed-off-by: NTony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/i40e/i40e_xsk.c

@@ -215,9 +215,7 @@ bool i40e_alloc_rx_buffers_zc(struct i40e_ring *rx_ring, u16 count)
 			bi = i40e_rx_bi(rx_ring, 0);
 			ntu = 0;
 		}
-
-		count--;
-	} while (count);
+	} while (--count);
 
 no_buffers:
 	if (rx_ring->next_to_use != ntu) {