arm: Fix uninitialised warning with gcc 4.8
arm: Fix uninitialised warning with gcc 4.8

Small fix for a warning that prevents compilation with gcc 4.8.1 due
to detecting that a variable might be uninitialised. The fix is to
assign a safe default.

hoangt/tpzsimul.gem5,vovojh/gem5,vovojh/gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,vovojh/gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,vovojh/gem5,vovojh/gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-