fp5280g2: replace --enable-use_json by --enable-use-json

For consistency, use hyphen and not a mix of underscore and hyphen.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ic127a65734ad5448d3d8aa312ad3aef71fb86688
diff --git a/meta-fp5280g2/recipes-phosphor/leds/phosphor-led-manager_%.bbappend b/meta-fp5280g2/recipes-phosphor/leds/phosphor-led-manager_%.bbappend
index a122a72..2ad194f 100644
--- a/meta-fp5280g2/recipes-phosphor/leds/phosphor-led-manager_%.bbappend
+++ b/meta-fp5280g2/recipes-phosphor/leds/phosphor-led-manager_%.bbappend
@@ -2,7 +2,7 @@
 
 SRC_URI += "file://led-group-config.json"
 
-EXTRA_OECONF = "--enable-use_json"
+EXTRA_OECONF += "--enable-use-json"
 
 DEPENDS += "phosphor-dbus-interfaces"