crimson/os/seastore: use map::emplace(key, val) instead of map::emplace(pair<>)

simpler this way.

Signed-off-by: Kefu Chai <kchai@redhat.com>

src/crimson/os/seastore/seastore.cc

@@ -418,9 +418,8 @@ SeaStore::_omap_get_values_ret SeaStore::_omap_get_values(
 		  bufferlist bl;
 		  bl.append(*p);
 		  ret.emplace(
-		    std::make_pair(
-		      std::move(key),
-		      std::move(bl)));
+		    std::move(key),
+		    std::move(bl));
 		}
 		return seastar::now();
 	      });