egl/wayland: fix dri2_initialize_wayland_drm memory leak

Hi all,

I'm trying to learn a bit more about Mesa and this is my first contribution. I hope I didn't make any obvious mistake:

When "dri2_wl_formats_init" fails in "dri2_initialize_wayland_drm", the "dri2_egl_display" is leaked because is not associated with the display yet.

Reported by Coverity Scan: https://scan5.coverity.com/reports.htm#v56945/p10037/fileInstanceId=204539064&defectInstanceId=52301906&mergedDefectId=1494541