[XFS] clean up the xfs_offset_to_map interface Currently we pass a struct

page and a relative offset into that page around, and returns the current
xfs_iomap_t if the block at the specified offset fits into it, or a NULL
pointer otherwise.  This patch passed the full 64bit offset into the inode
that all callers have anyway, and changes the return value to a simple
boolean.  Also the function gets a more descriptive name: xfs_iomap_valid.

SGI-PV: 947118
SGI-Modid: xfs-linux-melb:xfs-kern:203825a

Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>