soc: qcom: Correct idle task check for stack capture

Correct the idle task check, to be done on 'next'
task, instead of current task, while registering
current task's stack.

Change-Id: I8c4fde434b3eca0543c5748234ebabbd40da8672
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>