locktorture: fix deadlock in 'rw_lock_irq' type

torture_rwlock_read_unlock_irq() must use read_unlock_irqrestore()
instead of write_unlock_irqrestore().

Use read_unlock_irqrestore() instead of write_unlock_irqrestore().

Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>