[GFS2] Clean up internal read function

As requested by Christoph, this patch cleans up GFS2's internal
read function so that it no longer uses the do_generic_mapping_read
function. This function is obsolete and GFS2 is the last user of it.

As a side effect the internal read code gets smaller and easier
to read and gfs2_readpage is split into two. One function has the locking
and the other function has the rest of the logic.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>

fs/gfs2/rgrp.c

@@ -25,10 +25,10 @@
 #include "rgrp.h"
 #include "super.h"
 #include "trans.h"
-#include "ops_file.h"
 #include "util.h"
 #include "log.h"
 #include "inode.h"
+#include "ops_address.h"
 
 #define BFITNOENT ((u32)~0)
 #define NO_BLOCK ((u64)~0)