[fix]fix tmpfs bug (#8970)

* first

* second

* thrid

* Update SConscript

* tmpfs testcase default n

* Update dfs_tmpfs.c

* format document

---------

Co-authored-by: zhujiale <zhujiale@rt-thread.com>

examples/utest/testcases/tmpfs/SConscript

@@ -0,0 +1,13 @@
+Import('rtconfig')
+from building import *
+
+cwd     = GetCurrentDir()
+src     = []
+CPPPATH = [cwd]
+
+if GetDepend(['RT_USING_SMART','UTEST_TMPFS_CP']):
+    src += ['tmpfs.c']
+
+group = DefineGroup('utestcases', src, depend = ['RT_USING_UTESTCASES'], CPPPATH = CPPPATH)
+
+Return('group')