p7821: fix test_perf invocation for prereqs

Since 5dccd91 (t/perf: add iteration setup mechanism to perf-lib,
2022-04-04), perf tests need to declare their prerequisites with
'--prereq', after the test title. p7821 was forgotten in that commit,
such that running that test on a machine where the PCRE prereq is not
satisfied aborts the test with:

    error: bug in the test script: test_wrapper_ needs 2 positional parameters

Fix this by correcting the two 'test_perf' invocations in that test
suite.

Signed-off-by: Philippe Blain <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: phil-blain

t/perf/p7821-grep-engines-fixed.sh

@@ -33,13 +33,13 @@ do
 		fi
 		if ! test_have_prereq PERF_GREP_ENGINES_THREADS
 		then
-			test_perf $prereq "$engine grep$GIT_PERF_7821_GREP_OPTS $pattern" "
+			test_perf "$engine grep$GIT_PERF_7821_GREP_OPTS $pattern" --prereq "$prereq" "
 				git -c grep.patternType=$engine grep$GIT_PERF_7821_GREP_OPTS $pattern >'out.$engine' || :
 			"
 		else
 			for threads in $GIT_PERF_GREP_THREADS
 			do
-				test_perf PTHREADS,$prereq "$engine grep$GIT_PERF_7821_GREP_OPTS $pattern with $threads threads" "
+				test_perf "$engine grep$GIT_PERF_7821_GREP_OPTS $pattern with $threads threads" --prereq "PTHREADS,$prereq" "
 					git -c grep.patternType=$engine -c grep.threads=$threads grep$GIT_PERF_7821_GREP_OPTS $pattern >'out.$engine.$threads' || :
 				"
 			done