fs cases: fix compile error

kernel/fs/cases/fs_stream_test.c:279:70: error: format ‘%zi’ expects argument of type ‘signed size_t’, but argument 4 has type ‘int’ [-Werror=format=]
  279 |           syslog(LOG_ERR, "len = %zi != return value from fwrite = %zi",
      |                                                                    ~~^
      |                                                                      |
      |                                                                      long int
      |                                                                    %i
  280 |                  len, ret);
      |                       ~~~
      |                       |
      |                       int
kernel/fs/cases/fs_stream_test.c:311:69: error: format ‘%zi’ expects argument of type ‘signed size_t’, but argument 4 has type ‘int’ [-Werror=format=]
  311 |           syslog(LOG_ERR, "len = %zi != return value from fread = %zi",
      |                                                                   ~~^
      |                                                                     |
      |                                                                     long int
      |                                                                   %i
  312 |                  len, ret);
      |                       ~~~
      |                       |
      |                       int

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

Author: Zhangshoukui

testing/testsuites/kernel/fs/cases/fs_stream_test.c

@@ -247,7 +247,7 @@ void test_nuttx_fs_stream03(FAR void **state)
   char *junk = "abcdefghijklmnopqrstuvwxyz";
   size_t len = strlen(junk);
   char *inbuf = NULL;
-  int ret;
+  size_t ret;
   int lc;
   for (lc = 0; lc < 10; lc++)
     {
@@ -264,7 +264,7 @@ void test_nuttx_fs_stream03(FAR void **state)
           assert_true(1 == 0);
         }
 
-      if ((size_t)ret != len)
+      if (ret != len)
         {
           syslog(LOG_ERR,
                  "len = %zi != return value from fwrite = %i",
@@ -297,7 +297,7 @@ void test_nuttx_fs_stream03(FAR void **state)
           assert_true(1 == 0);
         }
 
-      if ((size_t)ret != len)
+      if (ret != len)
         {
           syslog(LOG_ERR,
                  "len = %zi != return value from fread = %i",