MDEV-31309 Innodb_buffer_pool_read_requests is not updated correctly

srv_export_innodb_status(): Update
export_vars.innodb_buffer_pool_read_requests as it was done
before commit a55b951e (MDEV-26827).
If innodb_status_variables[] pointed to a sharded variable, it would
only access the first shard.

storage/innobase/handler/ha_innodb.cc

@@ -946,7 +946,8 @@ static SHOW_VAR innodb_status_variables[]= {
   {"buffer_pool_read_ahead", &buf_pool.stat.n_ra_pages_read, SHOW_SIZE_T},
   {"buffer_pool_read_ahead_evicted",
    &buf_pool.stat.n_ra_pages_evicted, SHOW_SIZE_T},
-  {"buffer_pool_read_requests", &buf_pool.stat.n_page_gets, SHOW_SIZE_T},
+  {"buffer_pool_read_requests",
+   &export_vars.innodb_buffer_pool_read_requests, SHOW_SIZE_T},
   {"buffer_pool_reads", &buf_pool.stat.n_pages_read, SHOW_SIZE_T},
   {"buffer_pool_wait_free", &buf_pool.stat.LRU_waits, SHOW_SIZE_T},
   {"buffer_pool_write_requests",

storage/innobase/include/srv0srv.h

@@ -674,6 +674,8 @@ struct export_var_t{
 #ifdef UNIV_DEBUG
 	ulint innodb_buffer_pool_pages_latched;	/*!< Latched pages */
 #endif /* UNIV_DEBUG */
+	/** buf_pool.stat.n_page_gets (a sharded counter) */
+	ulint innodb_buffer_pool_read_requests;
 	ulint innodb_buffer_pool_write_requests;/*!< srv_stats.buf_pool_write_requests */
 	ulint innodb_checkpoint_age;
 	ulint innodb_checkpoint_max_age;

storage/innobase/srv/srv0srv.cc

@@ -1011,6 +1011,9 @@ srv_export_innodb_status(void)
 	export_vars.innodb_data_written = srv_stats.data_written
 		+ (dblwr << srv_page_size_shift);
 
+	export_vars.innodb_buffer_pool_read_requests
+		= buf_pool.stat.n_page_gets;
+
 	export_vars.innodb_buffer_pool_write_requests =
 		srv_stats.buf_pool_write_requests;