Fix a typo in the help message.

sql/mysqld.cc:
  Fix a typo.

sql/mysqld.cc

@@ -5253,7 +5253,7 @@ The minimum value for this variable is 4096.",
     (gptr*) &max_system_variables.max_length_for_sort_data, 0, GET_ULONG,
     REQUIRED_ARG, 1024, 4, 8192*1024L, 0, 1, 0},
   {"max_prepared_stmt_count", OPT_MAX_PREPARED_STMT_COUNT,
-   "Maximum numbrer of prepared statements in the server.",
+   "Maximum number of prepared statements in the server.",
    (gptr*) &max_prepared_stmt_count, (gptr*) &max_prepared_stmt_count,
    0, GET_ULONG, REQUIRED_ARG, 16382, 0, 1*1024*1024, 0, 1, 0},
   {"max_relay_log_size", OPT_MAX_RELAY_LOG_SIZE,