FruDevice: Define the day 1/1/96.

FruDevice should decide the first day of the month. Otherwise, the date on its
own dbus-object gets different from the result of ipmitool.

Tested:
After applying this patch, the date on the dbus-object is the same as what
ipmitool shows.

For example:
root@xxx:/usr/bin# busctl get-property xyz.openbmc_project.FruDevice \
> /xyz/openbmc_project/FruDevice/xxx xyz.openbmc_project.FruDevice \
> BOARD_MANUFACTURE_DATE
s "2020-09-24 - 06:25:00"
root@xxx:/usr/bin# ipmitool fru print 132 | grep "Date"
 Board Mfg Date        : Thu Sep 24 06:25:00 2020 UTC

Signed-off-by: Scron-Chang <Scron.Chang@quantatw.com>
Change-Id: Ic0ed37f18661bafff26676027dc5e16743968221
diff --git a/src/FruUtils.cpp b/src/FruUtils.cpp
index 32647d9..9e0170f 100644
--- a/src/FruUtils.cpp
+++ b/src/FruUtils.cpp
@@ -39,6 +39,7 @@
 {
     std::tm val = {};
     val.tm_year = 1996 - 1900;
+    val.tm_mday = 1;
     return val;
 }