grep/pcre2: prepare to add debugging to pcre2_malloc()

Change pcre2_malloc() in a way that'll make it easier for a debugging
fprintf() to spew out the allocated pointer.

This doesn't introduce any functional change, it just makes a
subsequent commit's diff easier to read. Changes code added in
513f2b0bbd4 (grep: make PCRE2 aware of custom allocator, 2019-10-16).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

grep.c

@@ -45,7 +45,8 @@ static pcre2_general_context *pcre2_global_context;
 
 static void *pcre2_malloc(PCRE2_SIZE size, MAYBE_UNUSED void *memory_data)
 {
-	return malloc(size);
+	void *pointer = malloc(size);
+	return pointer;
 }
 
 static void pcre2_free(void *pointer, MAYBE_UNUSED void *memory_data)