Key increment scripts: fix incrementing keys not in $PWD

Part of the recent rewrite dropped changing of the active dir to
${KEY_DIR}.  Meant the scripts needed to be run inside of the key
dir since not all functions take the key dir as an argument but
instead assume they're in ${PWD}.

BUG=None
TEST=Ran increment_kernel_subkey_and_key_mp.sh and saw it work
BRANCH=None

Change-Id: Icbc02f123e999d186d9c40fd16528a134397699e
Reviewed-on: https://gerrit.chromium.org/gerrit/35803
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/keygeneration/common.sh b/scripts/keygeneration/common.sh
index b7725ad..c3c1c25 100755
--- a/scripts/keygeneration/common.sh
+++ b/scripts/keygeneration/common.sh
@@ -125,6 +125,8 @@
 # Loads the current versions prints them to stdout and sets the global version
 # variables: CURR_FIRMKEY_VER CURR_FIRM_VER CURR_KERNKEY_VER CURR_KERN_VER
 load_current_versions() {
+  local key_dir=$1
+  local VERSION_FILE="${key_dir}/${VERSION_FILE}"
   if [[ ! -f ${VERSION_FILE} ]]; then
     return 1
   fi