e2e: validate the error return instead of object for consitency

If loadPVC() fails, it return error and we expect the PVC object
to be nil too. In many places we check on the error and exit.
However in few places we are looking at PVC object.
This commit make the condition check on `err` instead of `PVC`
object for consistency.

Signed-off-by: Humble Chirammal <hchiramm@redhat.com>

e2e/upgrade-rbd.go

@@ -160,7 +160,7 @@ var _ = Describe("RBD Upgrade Testing", func() {
 				data := "check data persists"
 
 				pvc, err = loadPVC(pvcPath)
-				if pvc == nil {
+				if err != nil {
 					e2elog.Failf("failed to load pvc with error %v", err)
 				}
 				pvc.Namespace = f.UniqueName