configure.ac: Use ${datarootdir} for --with-vulkan-icddir help string too

The help string wasn't updated in cbc37f7.

Fixes: cbc37f7 ("anv: install the intel_icd.json to ${datarootdir} by
default")

Signed-off-by: Andreas Boll <andreas.boll.dev@gmail.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Cc: mesa-stable@lists.freedesktop.org
1 file changed