uart: Works better if we actually allocate out_buf
uart: Works better if we actually allocate out_buf

That got lost during a rebase ... oops.

Signed-off-by: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>

open-power/skiboot,cyrilbur-ibm/skiboot,stewart-ibm/skiboot,cyrilbur-ibm/skiboot,ddstreet/skiboot,qemu/skiboot,neelegup/skiboot,legoater/skiboot,jk-ozlabs/skiboot,open-power/skiboot,shenki/skiboot,mikey/skiboot,mikey/skiboot,ddstreet/skiboot,cyrilbur-ibm/skiboot,neelegup/skiboot,csmart/skiboot,jk-ozlabs/skiboot,apopple/skiboot,jk-ozlabs/skiboot,shenki/skiboot,qemu/skiboot,stewart-ibm/skiboot,qemu/skiboot,apopple/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,apopple/skiboot,shenki/skiboot,open-power/skiboot,stewart-ibm/skiboot,legoater/skiboot,csmart/skiboot,legoater/skiboot,qemu/skiboot,open-power/skiboot,legoater/skiboot,mikey/skiboot,shenki/skiboot,qemu/skiboot,neelegup/skiboot,ddstreet/skiboot,csmart/skiboot