client: Fix inode remove from snaprealm race

This is a follow on fix to b5ce4d0.  Always remove the inode from the
snaprealm's list of inodes_with_caps before the snaprealm ref is
decremented (and the snaprealm potentially gets freed).

Fixes #4694.
Signed-off-by: Sam Lang <sam.lang@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>