NFC: trf7970a: Remove incorrect of_node_put() call

of_property_read_u32() does not take a reference
to the specified OF node so don't call of_node_put()
in trf7970a_get_autosuspend_delay().

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>