ltp: fix review questions

Signed-off-by: yangyalei <yangyalei@xiaomi.com>

libs/libc/signal/sig_altstack.c

@@ -41,7 +41,7 @@
  *
  ****************************************************************************/
 
-int sigaltstack(const stack_t *ss, stack_t *oss)
+int sigaltstack(FAR const stack_t *ss, FAR stack_t *oss)
 {
   if (ss)
     {

libs/libc/string/lib_strsignal.c

@@ -98,6 +98,7 @@ FAR char *strsignal(int signum)
       CASE_SIG_STR(SIGXFSZ,   "File size limit exceeded");
       CASE_SIG_STR(SIGVTALRM, "Virtual timer expired");
       CASE_SIG_STR(SIGPROF,   "Profiling timer expired");
+      CASE_SIG_STR(SIGWINCH,  "Window resize signal");
       CASE_SIG_STR(SIGPOLL,   "Pollable event occurred");
       CASE_SIG_STR(SIGSYS,    "Bad system call");
 

mm/umm_heap/umm_malloc.c

@@ -62,7 +62,7 @@ FAR void *malloc(size_t size)
   /* Use mm_malloc() because it implements the clear */
 
   ret = mm_malloc(USR_HEAP, size);
-  if (!ret)
+  if (ret == NULL)
     {
       set_errno(ENOMEM);
     }

mm/umm_heap/umm_memalign.c

@@ -89,7 +89,7 @@ FAR void *memalign(size_t alignment, size_t size)
   FAR void *ret;
 
   ret = mm_memalign(USR_HEAP, alignment, size);
-  if (!ret)
+  if (ret == NULL)
     {
       set_errno(ENOMEM);
     }

mm/umm_heap/umm_realloc.c

@@ -91,7 +91,7 @@ FAR void *realloc(FAR void *oldmem, size_t size)
   FAR void *ret;
 
   ret = mm_realloc(USR_HEAP, oldmem, size);
-  if (!ret)
+  if (ret == NULL)
     {
       set_errno(ENOMEM);
     }

mm/umm_heap/umm_zalloc.c

@@ -68,7 +68,7 @@ FAR void *zalloc(size_t size)
   /* Use mm_zalloc() because it implements the clear */
 
   ret = mm_zalloc(USR_HEAP, size);
-  if (!ret)
+  if (ret == NULL)
     {
       set_errno(ENOMEM);
     }