egl/drm: fix EGL_EXT_buffer_age with gbm contexts
Fix remaining dri2 check from 3d59f4cf, which caused gbm contexts to not expose EGL_EXT_buffer_age anymore.
Reference: !24347 (comment 2037087)
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Fix remaining dri2 check from 3d59f4cf, which caused gbm contexts to not expose EGL_EXT_buffer_age anymore.
Reference: !24347 (comment 2037087)