vol: Restore inode OS_READ/WRITE

vol: Restore inode OS_READ/WRITE

Commit 335ccb4082657b7d0e4e9af1076356cf115642d2 removed the OS_READ
and OS_WRITE definitions for non-namei code. We need those definitions
to build the pread/pwrite emulation functions, so put them back in.
This allows us to build the inode fileserver backend when we do not
have native positional I/O.

Change-Id: I3c066dacbee20301b38f074142cb6b6bb6b05de7
Reviewed-on: http://gerrit.openafs.org/3959
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>