ANDROID: fuse-bpf: Rename iocb_fuse to iocb_orig

The current name is a bit confusing. iocb_fuse could refer to the iocb
passed to fuse or created by fuse. The new name unambiguously refers to
the one passed in to fuse.

Test: compiles, behavior unchanged
Bug: 217570523
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Change-Id: I955500eb8a3186252427fd06ca6e99b4fec469b6