From: Yue Hu <huyue2@xxxxxxxxxxx>
No need end parameter since it's pointless for !backmost, we can get it
for backmost internally. And we only expand the trailing edge, so the
newstart can be replaced with ->headoffset.
Also, remove linux/prefetch.h that is not used anymore after commit
386292919c25 ("erofs: introduce readmore decompression strategy").
Signed-off-by: Yue Hu <huyue2@xxxxxxxxxxx>