power: reset: qcom-dload-mode: nodump mode error handling

In case nodump mode is already set, do not allow user to
change dump mode to other modes now.

Change-Id: I25b9e0d20b4dca2fb19d22f225a3dd9f0ea66cc5
Signed-off-by: Khaja Hussain Shaik Khaji <quic_kshaikkh@quicinc.com>