tests: kernel: Don't use VLA in pipe_api test.

In the current pipe_api test file we inadvertantly use VLA.
Toolchains are allowed by standard to allocate VLA on
heap for example. Therefore in my opinion we shouldn't
use VLA atleast in kernel+kernel tests.

Signed-off-by: Robin Kastberg <[email protected]>

Author: RobinKastberg

tests/kernel/pipe/pipe_api/src/stress.c

@@ -11,6 +11,9 @@
 #include <zephyr/random/random.h>
 #include <zephyr/timing/timing.h>
 
+#define WRITE_LEN 512
+#define READ_LEN  512
+
 LOG_MODULE_REGISTER(k_k_pipe_stress, LOG_LEVEL_INF);
 
 ZTEST_SUITE(k_pipe_stress, NULL, NULL, NULL, NULL, NULL);
@@ -19,9 +22,9 @@ ZTEST(k_pipe_stress, test_write)
 {
 	int rc;
 	struct k_pipe pipe;
-	size_t len = 512;
-	uint8_t buffer[len];
-	uint8_t buf[len];
+	const size_t len = WRITE_LEN;
+	uint8_t buffer[WRITE_LEN];
+	uint8_t buf[WRITE_LEN];
 	size_t sent;
 	uint32_t start_cycles, end_cycles;
 
@@ -41,9 +44,9 @@ ZTEST(k_pipe_stress, test_read)
 {
 	int rc;
 	struct k_pipe pipe;
-	size_t len = 512;
-	uint8_t buffer[len];
-	uint8_t buf[len];
+	const size_t len = READ_LEN;
+	uint8_t buffer[READ_LEN];
+	uint8_t buf[READ_LEN];
 	size_t sent, read;
 	uint32_t start_cycles, end_cycles;