meta-facebook: bletchley: add valid virtual-sensor config

phosphor-virtual-sensors was crashing on bletchley due to an
empty file, which is invalid JSON.  Add a valid JSON file,
which is just an empty array, instead.

Tested: Ran in QEMU and ensured service no longer crashes.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ibf30771a158344cbce519260d44ea945a0e12723
diff --git a/meta-facebook/recipes-phosphor/sensors/phosphor-virtual-sensor/bletchley/bletchley_sensor_config.json b/meta-facebook/recipes-phosphor/sensors/phosphor-virtual-sensor/bletchley/bletchley_sensor_config.json
index e69de29..fe51488 100644
--- a/meta-facebook/recipes-phosphor/sensors/phosphor-virtual-sensor/bletchley/bletchley_sensor_config.json
+++ b/meta-facebook/recipes-phosphor/sensors/phosphor-virtual-sensor/bletchley/bletchley_sensor_config.json
@@ -0,0 +1 @@
+[]