tableam: Fix index_build_range_scan parameter name.

All of the other code thinks that the 8th parameter is the number of
blocks, but this declaration thinks that it's the ending block number.
Repair this inconsistency.

Patch by me, reviewed by Andres Freund.

Discussion: http://postgr.es/m/CA+TgmoY49ManQWnJtiwkuytXBkmyTuDFqb74Pr4Zn2Nq9TuNBQ@mail.gmail.com

src/include/access/tableam.h

@@ -543,7 +543,7 @@ typedef struct TableAmRoutine
 										   bool anyvisible,
 										   bool progress,
 										   BlockNumber start_blockno,
-										   BlockNumber end_blockno,
+										   BlockNumber numblocks,
 										   IndexBuildCallback callback,
 										   void *callback_state,
 										   TableScanDesc scan);