[macos] Fixed compilation error (#6690)

Followup to last-minute refactoring in #6637.

platform/macos/src/NSImage+MGLAdditions.mm

@@ -2,14 +2,13 @@
 
 @implementation NSImage (MGLAdditions)
 
-- (std::unique_ptr<mbgl::SpriteImage>)mgl_spriteImage
-{
+- (std::unique_ptr<mbgl::SpriteImage>)mgl_spriteImage {
     // Create a bitmap image representation from the image, respecting backing
     // scale factor and any resizing done on the image at runtime.
     // http://www.cocoabuilder.com/archive/cocoa/82430-nsimage-getting-raw-bitmap-data.html#82431
-    [image lockFocus];
+    [self lockFocus];
     NSBitmapImageRep *rep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:{ NSZeroPoint, self.size }];
-    [image unlockFocus];
+    [self unlockFocus];
 
     // Get the image’s raw pixel data as an RGBA buffer.
     std::string pixelString((const char *)rep.bitmapData, rep.pixelsWide * rep.pixelsHigh * 4 /* RGBA */);
@@ -17,7 +16,7 @@
     mbgl::PremultipliedImage cPremultipliedImage(rep.pixelsWide, rep.pixelsHigh);
     std::copy(rep.bitmapData, rep.bitmapData + cPremultipliedImage.size(), cPremultipliedImage.data.get());
     return std::make_unique<mbgl::SpriteImage>(std::move(cPremultipliedImage),
-      (float)(rep.pixelsWide / self.size.width));
+                                               (float)(rep.pixelsWide / self.size.width));
 }
 
 @end