drivers: of-thermal: Handle krealloc failure correctly

Update the krealloc failure check to catch the failure in memory
allocation. The existing check triggers a false positive and exits
when the allocation has succeeded.

Change-Id: If85762cce85139750b7d7385a03b0e0db2100733
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>