Fix error message for topkeys parameter parsing

The wrong field name was returned

Change-Id: Ibb740f6adf11469baaa5f8ed13e99c708092cf2d
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/239903
Reviewed-by: Paolo Cocchi <paolo.cocchi@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>

Author: trondn

daemon/ioctl.cc

@@ -349,7 +349,7 @@ static cb::engine_errc ioctlSetTopkeysStart(Cookie& cookie,
                 return cb::engine_errc::invalid_arguments;
             }
         } catch (const std::exception&) {
-            cookie.setErrorContext("Failed to parse limit argument");
+            cookie.setErrorContext("Failed to parse shards argument");
             return cb::engine_errc::invalid_arguments;
         }
     }