f2fs: factor the read/write tracing logic into a helper

[ Upstream commit a28bca0f ]

Factor the logic to log a path for reads and writs into a helper
shared between the read_iter and write_iter methods.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Stable-dep-of: 0cac5118 ("f2fs: fix to avoid racing in between read and OPU dio write")
Signed-off-by: Sasha Levin <sashal@kernel.org>