sst: Initialize OsMailboxCommand status

Static analyzer raised an issue on this unitialized member. It's not an
issue in current usage of the struct, but in theory the success()
function would have UB for OsMailboxCommands created with a Throw error
policy.

Change-Id: I16650173add98efecc96535f30c90132481cf231
Signed-off-by: Jonathan Doman <jonathan.doman@intel.com>
diff --git a/src/sst_mailbox.cpp b/src/sst_mailbox.cpp
index 418f3fe..2627894 100644
--- a/src/sst_mailbox.cpp
+++ b/src/sst_mailbox.cpp
@@ -261,7 +261,7 @@
     };
 
     uint32_t value;
-    PECIManager::MailboxStatus status;
+    PECIManager::MailboxStatus status = PECIManager::MailboxStatus::NoError;
     /**
      * Construct the command object with required PECI address and up to 4
      * optional 1-byte input data parameters.