scripts: coccicheck: Add quotes to improve portability

While fetching the number of threads per core with lscpu,
the [:digit:] set is used for translation of digits from 0-9.
However, using [:digit:] instead of "[:digit:]" does not seem
to work uniformly for some shell types and configurations
(such as zsh).

Therefore, modify coccicheck to use double quotes around the
[:digit:] set for uniformity and better portability.
Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

scripts/coccicheck

@@ -76,7 +76,7 @@ else
     fi
 
     # Use only one thread per core by default if hyperthreading is enabled
-    THREADS_PER_CORE=$(lscpu | grep "Thread(s) per core: " | tr -cd [:digit:])
+    THREADS_PER_CORE=$(lscpu | grep "Thread(s) per core: " | tr -cd "[:digit:]")
     if [ -z "$J" ]; then
         NPROC=$(getconf _NPROCESSORS_ONLN)
 	if [ $THREADS_PER_CORE -gt 1 -a $NPROC -gt 2 ] ; then