shared/platform.h: use weston_check_egl_extension over strstr

The later can give false positives.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
diff --git a/shared/platform.h b/shared/platform.h
index 77c8259..e0ed55b 100644
--- a/shared/platform.h
+++ b/shared/platform.h
@@ -88,9 +88,9 @@
 {
 	const char *extensions = eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);
 
-	if (extensions
-	    && (strstr(extensions, "EGL_EXT_platform_wayland")
-	        || strstr(extensions, "EGL_KHR_platform_wayland"))) {
+	if (extensions &&
+	    (weston_check_egl_extension(extensions, "EGL_EXT_platform_wayland") ||
+	     weston_check_egl_extension(extensions, "EGL_KHR_platform_wayland"))) {
 		return (void *) eglGetProcAddress(address);
 	}