Fix "possibly uninitialized variable"

Compiling with GCOV causes the variable_buffer::flipBit() function
to be analyzed differently than without, resulting in a warning for
the possibly-uninitialized variable and causing compilation failure
when the -Werror option is enabled. This commit explicitly initializes
the variable.

Change-Id: Idc59ba411cc1f9200888bba6c215e48bb7051b7c
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/78485
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: PPE CI <ppe-ci+hostboot@us.ibm.com>
Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
Tested-by: HWSV CI <hwsv-ci+hostboot@us.ibm.com>
Reviewed-by: Nicholas E. Bofferding <bofferdn@us.ibm.com>
Reviewed-by: Ilya Smirnov <ismirno@us.ibm.com>
Reviewed-by: Jennifer A Stofer <stofer@us.ibm.com>
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/78513
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>

src/import/hwpf/fapi2/include/variable_buffer.H

@@ -5,7 +5,7 @@
 /*                                                                        */
 /* OpenPOWER HostBoot Project                                             */
 /*                                                                        */
-/* Contributors Listed Below - COPYRIGHT 2015,2017                        */
+/* Contributors Listed Below - COPYRIGHT 2015,2019                        */
 /* [+] International Business Machines Corp.                              */
 /*                                                                        */
 /*                                                                        */
@@ -475,7 +475,7 @@ class variable_buffer
         ///
         inline fapi2::ReturnCodes flipBit( bits_type SB, bits_type L = 1)
         {
-            ReturnCodes rc;
+            ReturnCodes rc = FAPI2_RC_SUCCESS;
 
             // make sure we are within our container
             if((SB + L) <= this->iv_perceived_bit_length)