fdt: Update fdt_test to use 'dt' instead of 'fdt'

Since fdt is a module it conflicts with this variable name and prevents it
being used in tests. Rename the variable.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/fdt_test.py b/tools/binman/fdt_test.py
index 1d9494e..12edeab 100644
--- a/tools/binman/fdt_test.py
+++ b/tools/binman/fdt_test.py
@@ -28,21 +28,21 @@
     def GetCompiled(self, fname):
         return fdt_util.EnsureCompiled(self.TestFile(fname))
 
-    def _DeleteProp(self, fdt):
-        node = fdt.GetNode('/microcode/update@0')
+    def _DeleteProp(self, dt):
+        node = dt.GetNode('/microcode/update@0')
         node.DeleteProp('data')
 
     def testFdtNormal(self):
         fname = self.GetCompiled('34_x86_ucode.dts')
-        fdt = FdtScan(fname)
-        self._DeleteProp(fdt)
+        dt = FdtScan(fname)
+        self._DeleteProp(dt)
 
     def testFdtFallback(self):
         fname = self.GetCompiled('34_x86_ucode.dts')
-        fdt = FdtScan(fname, True)
-        fdt.GetProp('/microcode/update@0', 'data')
+        dt = FdtScan(fname, True)
+        dt.GetProp('/microcode/update@0', 'data')
         self.assertEqual('fred',
-            fdt.GetProp('/microcode/update@0', 'none', default='fred'))
+            dt.GetProp('/microcode/update@0', 'none', default='fred'))
         self.assertEqual('12345678 12345679',
-            fdt.GetProp('/microcode/update@0', 'data', typespec='x'))
-        self._DeleteProp(fdt)
+            dt.GetProp('/microcode/update@0', 'data', typespec='x'))
+        self._DeleteProp(dt)