qseecom : Pass proper device node pointer

Pass proper device node pointer to
of_reserved_mem_device_init_by_idx so that
it contains the of_node data which is needed
by the api.

Change-Id: I327f95657628eaa2e0e4bf98a919e003cdae7a86
Signed-off-by: Anmolpreet Kaur <anmolpre@codeaurora.org>