iomap: Spelling s/preceeding/preceding/g

Fix a misspelling of "preceding".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>