meta-google: phosphor-ipmi-config: remove bash-ism

Use POSIX-standard `[` instead of bash-specific `[[`.

Tested: No change to entity-map.json

Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Change-Id: I0097ac6317e093f4eddecf5d2a33fdd8cf48ffe8
diff --git a/meta-google/recipes-phosphor/ipmi/phosphor-ipmi-config.bbappend b/meta-google/recipes-phosphor/ipmi/phosphor-ipmi-config.bbappend
index 6e25fc2..6d93c27 100644
--- a/meta-google/recipes-phosphor/ipmi/phosphor-ipmi-config.bbappend
+++ b/meta-google/recipes-phosphor/ipmi/phosphor-ipmi-config.bbappend
@@ -62,7 +62,7 @@
 
   # Set entity-map.json to empty json for gBMC by default.
   # Each system will override it if needed.
-  if [[ "${ENTITY_MAPPING}" != "default" ]]; then
+  if [ "${ENTITY_MAPPING}" != "default" ]; then
     echo "[]" > ${D}${datadir}/ipmi-providers/entity-map.json
   fi
 }