MdePkg:BaseArmTrngLibNull: Assert causing FVP stalling

FVP Base Revc doesn't support Trng.
ASSERT (FALSE) is causing the boot to stall.
Replacing ASSERT with ERROR log.

Signed-off-by: Prachotan Reddy Bathi <Prachotan.Bathi@arm.com>

MdePkg/Library/BaseArmTrngLibNull/BaseArmTrngLibNull.c

@@ -41,7 +41,7 @@ GetArmTrngVersion (
   OUT UINT16  *MinorRevision
   )
 {
-  ASSERT (FALSE);
+  DEBUG ((DEBUG_ERROR, "ArmTrng Backend not found\n"));
   return RETURN_UNSUPPORTED;
 }