egl: Update the comments to typecast macros.

Put a note that the macros define functions and should not be ended with
a semicolon when used.

src/egl/main/egldriver.h

@@ -8,6 +8,9 @@
 
 /**
  * Define an inline driver typecast function.
+ *
+ * Note that this macro defines a function and should not be ended with a
+ * semicolon when used.
  */
 #define _EGL_DRIVER_TYPECAST(drvtype, egltype, code)           \
    static INLINE struct drvtype *drvtype(const egltype *obj)   \
@@ -17,6 +20,9 @@
 /**
  * Define the driver typecast functions for _EGLDriver, _EGLDisplay,
  * _EGLContext, _EGLSurface, and _EGLConfig.
+ *
+ * Note that this macro defines several functions and should not be ended with
+ * a semicolon when used.
  */
 #define _EGL_DRIVER_STANDARD_TYPECASTS(drvname)                            \
    _EGL_DRIVER_TYPECAST(drvname ## _driver, _EGLDriver, obj)               \