wspoon: Apply offset to ambient temp sensor

According to thermal characterization, the ambient temperature sensor
requires a -2C offset applied to reflect the correct ambient
temperature.

Change-Id: I354988013d51ee57403fa68c3fa5120e59d16b74
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-phosphor/sensors/phosphor-hwmon%/obmc/hwmon/ahb/apb/i2c@1e78a000/i2c-bus@100/bmp280@77.conf b/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-phosphor/sensors/phosphor-hwmon%/obmc/hwmon/ahb/apb/i2c@1e78a000/i2c-bus@100/bmp280@77.conf
index e821950..cdf8b47 100644
--- a/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-phosphor/sensors/phosphor-hwmon%/obmc/hwmon/ahb/apb/i2c@1e78a000/i2c-bus@100/bmp280@77.conf
+++ b/meta-openbmc-machines/meta-openpower/meta-ibm/meta-witherspoon/recipes-phosphor/sensors/phosphor-hwmon%/obmc/hwmon/ahb/apb/i2c@1e78a000/i2c-bus@100/bmp280@77.conf
@@ -3,3 +3,4 @@
 WARNLO_temp1 = "0"
 CRITHI_temp1 = "35000"
 CRITLO_temp1 = "0"
+OFFSET_temp1 = "-2000"