i965: automake: correctly set MKDIR_GEN

Otherwise we might end up w/o the respective folder (depending on
autotools version) and fail at build time.

Fixes: bfd17c76c12 "i965: Port INTEL_PRECISE_TRIG=1 to NIR."
Cc: "12.0 13.0" <mesa-dev@lists.freedesktop.org>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit 5eed48d23780e812ca5c53fecc59a419962c7dd6)
1 file changed