Fix mac build, defined was not needed for IOS preprocessor

src/renderer_mtl.mm

@@ -235,7 +235,7 @@ namespace bgfx { namespace mtl
 		{ MTLPixelFormatInvalid,						MTLPixelFormatInvalid                       }, // ATC
 		{ MTLPixelFormatInvalid,						MTLPixelFormatInvalid                       }, // ATCE
 		{ MTLPixelFormatInvalid,						MTLPixelFormatInvalid                       }, // ATCI
-#if defined(BX_PLATFORM_IOS) && !defined(TARGET_OS_MACCATALYST)
+#if BX_PLATFORM_IOS && !defined(TARGET_OS_MACCATALYST)
 		{ MTLPixelFormatASTC_4x4_LDR,					MTLPixelFormatASTC_4x4_sRGB                 }, // ASTC4x4
 		{ MTLPixelFormatASTC_5x5_LDR,					MTLPixelFormatASTC_5x5_sRGB                 }, // ASTC5x5
 		{ MTLPixelFormatASTC_6x6_LDR,					MTLPixelFormatASTC_6x6_sRGB                 }, // ASTC6x6