uprobes: uprobes_treelock should not disable irqs

Nobody plays with uprobes_tree/uprobes_treelock in interrupt context,
no need to disable irqs.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>