perf tests coresight thread_loop_check_tid_2: Fix shellcheck warnings about word splitting/quoting

Running shellcheck on thread_loop_check_tid_2.sh throws below warning:

In tests/shell/coresight/thread_loop_check_tid_2.sh line 8:
. $(dirname $0)/../lib/coresight.sh
  ^-----------^ SC2046 (warning): Quote this to prevent word splitting.

Fixed the warning by adding quotes to avoid word splitting.
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230709182800.53002-24-atrajeev@linux.vnet.ibm.comSigned-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/coresight/thread_loop_check_tid_2.sh

@@ -5,7 +5,7 @@
 # Carsten Haitzler <carsten.haitzler@arm.com>, 2021
 
 TEST="thread_loop"
-. $(dirname $0)/../lib/coresight.sh
+. "$(dirname $0)"/../lib/coresight.sh
 ARGS="2 20"
 DATV="check-tid-2th"
 DATA="$DATD/perf-$TEST-$DATV.data"