wayland-egl: set the correct path to libwayland-egl.so

Earlier commit changed to passing the binary name as env. variable
introducing a typo.

That went unnoticed, since we do not check if the file is present or
not.

Cc: Pukka Paalanen <ppaalanen@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Fixes: 85cb5ed6 ("wayland-egl-symbols-check: pass the DSO name via
the build system")
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>