common/gnttab: Correct error handling for gnttab_setup_table()

common/gnttab: Correct error handling for gnttab_setup_table()

Simplify the error labels to just "unlock" and "out".  This fixes an erroneous
path where a failure of rcu_lock_domain_by_any_id() still results in
rcu_unlock_domain() being called.

This is only not an XSA by luck.  rcu_unlock_domain() is a nop other than
decrementing the preempt count, and nothing reads the preempt count outside of
a debug build.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>