selftests: cachestat: Fix warning on declaration under label

Fix warning caused from declaration under a case label. The proper way
is to declare variable at the beginning of the function. The warning
came from running clang using LLVM=1; and is as follows:

-test_cachestat.c:260:3: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
  260 |                 char *map = mmap(NULL, filesize, PROT_READ | PROT_WRITE,
      |

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sidharth Seela <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Reviewed-by: wang lian <[email protected]>
Reviewed-by: Dev Jain <[email protected]>
Acked-by: Shuah Khan <[email protected]>
Acked-by: Nhat Pham <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

Author: sidharth-458

tools/testing/selftests/cachestat/test_cachestat.c

@@ -226,7 +226,7 @@ bool run_cachestat_test(enum file_type type)
 	int syscall_ret;
 	size_t compute_len = PS * 512;
 	struct cachestat_range cs_range = { PS, compute_len };
-	char *filename = "tmpshmcstat";
+	char *filename = "tmpshmcstat", *map;
 	struct cachestat cs;
 	bool ret = true;
 	int fd;
@@ -257,7 +257,7 @@ bool run_cachestat_test(enum file_type type)
 		}
 		break;
 	case FILE_MMAP:
-		char *map = mmap(NULL, filesize, PROT_READ | PROT_WRITE,
+		map = mmap(NULL, filesize, PROT_READ | PROT_WRITE,
 				 MAP_SHARED, fd, 0);
 
 		if (map == MAP_FAILED) {