[Coverity CID :190957]Incorrect expression in /tests/kernel/fatal/src/main.c

[mandarcthorat1]

Static code scan issues seen in File: /tests/kernel/fatal/src/main.c
Category: Incorrect expression
Function: check_stack_overflow
Component: Tests
CID: 190957
Please fix or provide comments to square it off in coverity in the link: https://scan9.coverity.com/reports.htm#v32951/p12996

[andrewboie]

I set this in Coverity as a false positive, it thought there might be side effects of reading a volatile variable (in case it was some MMIO thing) but that wasn't the case here.