render/egl: don't fail on EGL_MESA_device_software
render/egl: don't fail on EGL_MESA_device_software

Mesa may advertise EGL_MESA_device_software even when hardware
drivers are in use [1]. Demote the error to a warning until the Mesa
bug is fixed.

[1]: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4178

References: https://github.com/swaywm/wlroots/pull/2689

SirCmpwn/wlroots,swaywm/wlroots,swaywm/wlroots