Fix build errors on Linux 5.1

Now support Linux versions 4.4.x, 4.9.x, 4.14.x, 4.18.x, 4.19.x, 4.20.x, 5.0.x, 5.1.x

os_dep/osdep_service.c

@@ -2201,7 +2201,6 @@ static int isFileReadable(const char *path, u32 *sz)
 		ret = PTR_ERR(fp);
 	else {
 		oldfs = get_fs();
-		set_fs(get_ds());
 
 		if (1 != readFile(fp, &buf, 1))
 			ret = PTR_ERR(fp);
@@ -2239,7 +2238,6 @@ static int retriveFromFile(const char *path, u8 *buf, u32 sz)
 			RTW_INFO("%s openFile path:%s fp=%p\n", __FUNCTION__, path , fp);
 
 			oldfs = get_fs();
-			set_fs(get_ds());
 			ret = readFile(fp, buf, sz);
 			set_fs(oldfs);
 			closeFile(fp);
@@ -2274,7 +2272,6 @@ static int storeToFile(const char *path, u8 *buf, u32 sz)
 			RTW_INFO("%s openFile path:%s fp=%p\n", __FUNCTION__, path , fp);
 
 			oldfs = get_fs();
-			set_fs(get_ds());
 			ret = writeFile(fp, buf, sz);
 			set_fs(oldfs);
 			closeFile(fp);