simplify initialising variables in shell scripts

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/update/blobs/inject

@@ -292,12 +292,10 @@ inject_blob_dell_e6400_vgarom_nvidia()
 inject_blob_smsc_sch5545_ec()
 {
 	rom="${1}"
-
 	_sch5545ec_location="${CONFIG_SMSC_SCH5545_EC_FW_FILE#../../}"
 
-	if [ ! -f "${_sch5545ec_location}" ]; then
+	[ -f "${_sch5545ec_location}" ] || \
 		err "inject_blob_smsc_sch5545_ec: SCH5545 fw missing"
-	fi
 
 	"${cbfstool}" "${rom}" add -f "${_sch5545ec_location}" \
 	    -n sch5545_ecfw.bin -t raw || \
@@ -307,12 +305,10 @@ inject_blob_smsc_sch5545_ec()
 modify_gbe()
 {
 	printf "changing mac address in gbe to ${new_mac}\n"
-
-	rom="${1}"
-
 	[ -z ${CONFIG_GBE_BIN_PATH} ] && \
 		err "modify_gbe: ${board}: CONFIG_GBE_BIN_PATH not set"
 
+	rom="${1}"
 	_gbe_location=${CONFIG_GBE_BIN_PATH#../../}
 
 	[ -f "${_gbe_location}" ] || \