scripts: checkpatch.pl: fix constant comparison false positives

Comparisons that have constants on both side of the operator
were getting flagged incorrectly. Adjust the check so that
pure constant comparisons are not flagged, reducing false
positives.

WARNING:CONSTANT_COMPARISON: \
  Comparisons should place the constant on the right side of \
  the test
+BUILD_ASSERT(CONFIG_MAX_PTHREAD_COUNT == \
  CONFIG_MAX_PTHREAD_MUTEX_COUNT - 1);

Signed-off-by: Christopher Friedt <cfriedt@meta.com>