iio: adc: versal-sysmon: fix write reg. in secure mode

commit 1626eacf72db0b5cbe7bcc57471978de4052479e from
https://github.com/Xilinx/linux-xlnx.git

 xlnx_rebase_v5.15

Fix write register method for secure mode.

Signed-off-by: Dragan Cvetic <dragan.cvetic@amd.com>
State: pending
Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>