pgsql: Update types in smgr API

Update types in smgr API

Change data buffer to void *, from char *, and add const where
appropriate.  This makes it match the File API (see also
2d4f1ba6cfc2f0a977f1c30bda9848041343e248) and stdio.

Discussion: https://www.postgresql.org/message-id/flat/11dda853-bb5b-59ba-a746-e168b1ce4bdb%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b9f0e54bc955ba3f6187d238b03c9c99c576a6af

Modified Files
--------------
contrib/bloom/blinsert.c              |  2 +-
src/backend/access/heap/rewriteheap.c |  4 ++--
src/backend/access/nbtree/nbtree.c    |  2 +-
src/backend/access/nbtree/nbtsort.c   |  6 +++---
src/backend/access/spgist/spginsert.c |  6 +++---
src/backend/storage/buffer/bufmgr.c   |  4 ++--
src/backend/storage/smgr/md.c         |  6 +++---
src/backend/storage/smgr/smgr.c       | 12 ++++++------
src/include/storage/md.h              |  6 +++---
src/include/storage/smgr.h            |  6 +++---
10 files changed, 27 insertions(+), 27 deletions(-)