MDEV-27014 InnoDB fails to restore page 0 from the doublewrite buffer

- Addressing the format issue in deferred_dblwr() and changed the
function comment.

storage/innobase/fsp/fsp0file.cc

@@ -438,10 +438,7 @@ Datafile::validate_for_recovery()
 		}
 
 		if (restore_from_doublewrite()) {
-			if (m_defer) {
-				return err;
-			}
-			return(DB_CORRUPTION);
+			return m_defer ? err : DB_CORRUPTION;
 		}
 
 		/* Free the previously read first page and then re-validate. */

storage/innobase/log/log0recv.cc

@@ -797,7 +797,10 @@ static struct
     return space;
   }
 
-  /* Recover the page0 of deferred tablespace from doublewrite buffer.*/
+  /** Attempt to recover pages from the doublewrite buffer.
+  This is invoked if we found neither a valid first page in the
+  data file nor redo log records that would initialize the first
+  page. */
   void deferred_dblwr()
   {
     for (auto d= defers.begin(); d != defers.end(); )