tidy: Simplify a number of boolean expressions.

The clang-tidy "simplify boolean expression" checker pointed out a one
place where expressions involving boolean values could be simplified.
These was a change from "while (b == true)" that can be reduced to
"while(b)" for easier reading.

https://clang.llvm.org/extra/clang-tidy/checks/readability-simplify-boolean-expr.html

mythtv/libs/libmythui/util-nvctrl.cpp

@@ -294,7 +294,7 @@ bool MythNVControl::GetNvidiaRates(MythXDisplay *MythDisplay, std::vector<Displa
                 break;
             }
         }
-    } while (erased == true);
+    } while (erased);
 
     // Update refresh rates
     for (size_t i = 0; i < VideoModes.size(); i++)