meta-aspeed: use OE shell variable style

OE convention (see OE-Core rev: f44bb4588) is for bitbake variables to
use braces and ordinary shell variables to not use braces.

Change-Id: I640076712f58d971b173849844215a64565a1d51
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 4dcbe40..5b90da1 100644
--- a/meta-aspeed/classes/socsec-sign.bbclass
+++ b/meta-aspeed/classes/socsec-sign.bbclass
@@ -37,10 +37,10 @@
             --algorithm ${SOCSEC_SIGN_ALGO} \
             --rsa_sign_key ${SOCSEC_SIGN_KEY} \
             --bl1_image ${DEPLOYDIR}/${SPL_IMAGE} \
-            ${signing_helper_args} \
+            $signing_helper_args \
             ${SOCSEC_SIGN_EXTRA_OPTS} \
             --output ${SPL_BINARY}.staged
-        cp -f ${SPL_BINARY}.staged ${B}/${CONFIG_B_PATH}/${SPL_BINARY}
+        cp -f ${SPL_BINARY}.staged ${B}/$CONFIG_B_PATH/${SPL_BINARY}
         mv -f ${SPL_BINARY}.staged ${DEPLOYDIR}/${SPL_IMAGE}
     fi
 }
@@ -49,8 +49,8 @@
     mkdir -p ${DEPLOYDIR}
     if [ -n "${UBOOT_CONFIG}" ]; then
         for config in ${UBOOT_MACHINE}; do
-            CONFIG_B_PATH="${config}"
-            cd ${B}/${config}
+            CONFIG_B_PATH="$config"
+            cd ${B}/$config
             sign_spl_helper
         done
     else