ceph_test_rados_api_tmap_migrate: fix warning

ceph_test_rados_api_tmap_migrate: fix warning

In file included from ./test/librados/TestCase.h:9:0,
                 from test/librados/tmap_migrate.cc:4:
../src/gmock/gtest/include/gtest/gtest.h: In instantiation of ‘testing::Asserti$
../src/gmock/gtest/include/gtest/gtest.h:1484:23:   required from ‘static testi$
test/librados/tmap_migrate.cc:56:3:   required from here
../src/gmock/gtest/include/gtest/gtest.h:1448:16: warning: comparison between s$
   if (expected == actual) {
                ^

Signed-off-by: Sage Weil <sage@redhat.com>