external/pflash: quote CROSS_COMPILE when passed to get_arch.sh
external/pflash: quote CROSS_COMPILE when passed to get_arch.sh

Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

mikey/skiboot,ddstreet/skiboot,open-power/skiboot,open-power/skiboot,qemu/skiboot,mikey/skiboot,shenki/skiboot,open-power/skiboot,csmart/skiboot,ddstreet/skiboot,stewart-ibm/skiboot,legoater/skiboot,csmart/skiboot,shenki/skiboot,qemu/skiboot,qemu/skiboot,stewart-ibm/skiboot,csmart/skiboot,shenki/skiboot,shenki/skiboot,qemu/skiboot,stewart-ibm/skiboot,apopple/skiboot,apopple/skiboot,legoater/skiboot,shenki/skiboot,legoater/skiboot,legoater/skiboot,open-power/skiboot,ddstreet/skiboot,apopple/skiboot,mikey/skiboot,legoater/skiboot,open-power/skiboot,qemu/skiboot