mds: fix broken EMetablob inode_t* return value

mds: fix broken EMetablob inode_t* return value

We pass this back to the caller, but it points to a member that is never
looked at, because the inode has already been encoded.  In effect this
wasn't journaling anything useful, and the only user questioned whether it
was needed, so let's rip it out.

Signed-off-by: Sage Weil <sage@inktank.com>