perf tests memcpy_thread_16k_10: Fix shellcheck warning about word splitting/quote

Running shellcheck on memcpy_thread_16k_10.sh throws below warning:

In memcpy_thread_16k_10.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.

ShellCheck result with patch:
    # shellcheck -S warning coresight/memcpy_thread_16k_10.sh
    #

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/20230709182800.53002-13-atrajeev@linux.vnet.ibm.com
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>