egl: fix EGL_EXT_protected_content/surface mixup
EGL_EXT_protected_surface introduces EGL_PROTECTED_CONTENT_EXT, while EGL_EXT_protected_content is about protected context.
When I implemented EGL_EXT_protected_surface I mixed up the 2 names, so this commit fixes it.
Fixes: bd182777 ("egl: implement EGL_EXT_protected_surface support")