Allocate immediately in _cogl_egl_texture_2d_new_from_image

The _cogl_egl_texture_2d_new_from_image function has a CoglError
argument which implies that it is unlike the other texture
constructors and returns errors immediately rather than having a
delayed-allocation mechanism. cogl_wayland_texture_2d_new_from_buffer
which calls it is also like this. We can't rely on delayed-allocation
semantics for this without changing the applications because the
texture needs to be allocated before the corresponding EGLImage is
destroyed. This patch just makes it immediately allocate.

A better patch might be to remove the error argument to make it
obvious that there are delayed-allocation semantics and then fix all
of the applications.

This was breaking Cogland and Mutter.

Reviewed-by: Robert Bragg <robert@linux.intel.com>