meta-aspeed: Use OE logging utilities

OE provides utilities for both warning and error messages, so use them.

Change-Id: I7548e09e69015dda4043d5aaa00a0c869393c595
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-aspeed/classes/socsec-sign.bbclass b/meta-aspeed/classes/socsec-sign.bbclass
index 06b14c0..4dcbe40 100644
--- a/meta-aspeed/classes/socsec-sign.bbclass
+++ b/meta-aspeed/classes/socsec-sign.bbclass
@@ -23,10 +23,9 @@
     signing_helper_args=""
 
     if [ "${SOC_FAMILY}" != "aspeed-g6" ] ; then
-        echo "Warning: SPL signing is only supported on AST2600 boards"
+        bbwarn "SPL signing is only supported on AST2600 boards"
     elif [ ! -e "${SOCSEC_SIGN_KEY}" ] ; then
-        echo "Error: Invalid socsec signing key: ${SOCSEC_SIGN_KEY}"
-        exit 1
+        bbfatal "Invalid socsec signing key: ${SOCSEC_SIGN_KEY}"
     else
         rm -f ${SPL_BINARY}.staged