scripts: fix false positive in commit check

It reports an false positive warning when the commit subject includes
the word "ctx", as it matches following regexp:

     -e 'rx\|tx\|RX\|TX'

Fixes: edbeb7d962e9 ("scripts: check commit formatting")

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

scripts/check-git-log.sh

@@ -86,8 +86,8 @@ bad=$(echo "$headlines" | grep \
 [ -z "$bad" ] || printf "Wrong headline uppercase:\n$bad\n"
 
 # check headline uppercase (Rx/Tx, VF, L2, MAC, Linux, ARM...)
-bad=$(echo "$headlines" | grep \
-	-e 'rx\|tx\|RX\|TX' \
+bad=$(echo "$headlines" | grep -E \
+	-e '\<(rx|tx|RX|TX)\>' \
 	-e '\<[pv]f\>' \
 	-e '\<l[234]\>' \
 	-e ':.*\<dma\>' \