test: Fix test apps linux port alloc size

This is a minor fix, as sys_sem_t is defined as
`typedef struct sys_sem * sys_sem_t;`
so the size is still the same (size of pointer)

Closes #54

test/apps/linux/sys_arch.c

@@ -663,7 +663,7 @@ sys_thread_sem_alloc(void)
  err_t err;
  int ret;
 
- sem = (sys_sem_t*)malloc(sizeof(sys_sem_t*));
+ sem = (sys_sem_t*)malloc(sizeof(sys_sem_t));
  LWIP_ASSERT("failed to allocate memory for TLS semaphore", sem != NULL);
  err = sys_sem_new(sem, 0);
  LWIP_ASSERT("failed to initialise TLS semaphore", err == ERR_OK);