Skip asking github for latest hash, if we're requesting a specific hash

Means one less call to curl in that scenario

rpi-update

@@ -376,16 +376,16 @@ command -v readelf >/dev/null 2>&1 || {
 	exit 1
 }
 
-# ask github for latest version hash
-REPO_API=${REPO_URI/github.com/api.github.com\/repos}/git/refs/heads/${BRANCH}
-GITREV=$(curl -Ls ${REPO_API} | awk '{ if ($1 == "\"sha\":") { print substr($2, 2, 40) } }')
-FW_REV=${FW_REV:-${GITREV}}
-
 if [[ "${FW_REV}" == "" ]]; then
-	echo " *** No hash received from github: ${REPO_API}"
-	# run again with errors not suppressed
-	curl -L ${REPO_API}
-	exit 1
+	# ask github for latest version hash
+	REPO_API=${REPO_URI/github.com/api.github.com\/repos}/git/refs/heads/${BRANCH}
+	FW_REV=$(curl -Ls ${REPO_API} | awk '{ if ($1 == "\"sha\":") { print substr($2, 2, 40) } }')
+	if [[ "${FW_REV}" == "" ]]; then
+		echo " *** No hash received from github: ${REPO_API}"
+		# run again with errors not suppressed
+		curl -L ${REPO_API}
+		exit 1
+	fi
 fi
 
 if [[ ! -f "${FW_REVFILE}" ]]; then