Fix errors in file cap_avfoundation.mm.
Compiled with Xcode 6.2, iOS SDK 8.2

Example:

cap_avfoundation.mm:543:54: error: cannot initialize a parameter of
type 'AVCaptureFocusMode' with an rvalue of type 'int'
    if ([mCaptureDevice isFocusModeSupported:(int)value]){
                                             ^~~~~~~~~~