ext4 extents: remove unneeded casts

There are many casts in extents.c which are not needed,
as the variables are already the type of the cast, or
are being promoted for no particular reason in printk's.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>