libweston: fix #ifdef ENABLE_EGL

Everywhere else uses #ifdef, this used just #if. When the next commit
adds -Wundef to the compiler options, this #if here will start failing
as ENABLE_EGL is undefined.

It would be much better to use Meson's set10() for ENABLE_EGL and change
all #ifdef into #if, but I opted for the smaller change for now.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/pixel-formats.c

@@ -38,7 +38,7 @@
 #include "wayland-util.h"
 #include "pixel-formats.h"
 
-#if ENABLE_EGL
+#ifdef ENABLE_EGL
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <GLES2/gl2.h>