i40evf: fix compiler warning of unused variable

BugLink: http://bugs.launchpad.net/bugs/1536474

Compiler complained of an unused variable, which the driver was just
using to store the result of a rd32 which is used to clear a register
unconditionally.  Just drop the unused variable and re-use one.
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit cfbe4dba)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/i40evf/i40evf_main.c

@@ -307,10 +307,9 @@ static irqreturn_t i40evf_msix_aq(int irq, void *data)
 	struct i40e_hw *hw = &adapter->hw;
 	u32 val;
 
-	/* handle non-queue interrupts */
-	rd32(hw, I40E_VFINT_ICR01);
-	rd32(hw, I40E_VFINT_ICR0_ENA1);
-
+	/* handle non-queue interrupts, these reads clear the registers */
+	val = rd32(hw, I40E_VFINT_ICR01);
+	val = rd32(hw, I40E_VFINT_ICR0_ENA1);
 
 	val = rd32(hw, I40E_VFINT_DYN_CTL01) |
 	      I40E_VFINT_DYN_CTL01_CLEARPBA_MASK;