module/sotest: Fix depends of SOTEST_BUILTINFS

Log:
  sotest_main.c: In function 'sotest_main':
  sotest_main.c:116:29: error: storage size of 'desc' isn't known
    116 |   struct boardioc_romdisk_s desc;
        |                             ^~~~
  sotest_main.c:116:29: error: unused variable 'desc' [-Werror=unused-variable]
  cc1: all warnings being treated as errors

Signed-off-by: wangjianyu3 <[email protected]>

Author: JianyuWang0623

examples/sotest/Kconfig

@@ -15,7 +15,7 @@ if EXAMPLES_SOTEST
 config EXAMPLES_SOTEST_BUILTINFS
 	bool "Built-in File System"
 	default y
-	depends on FS_ROMFS && BUILD_FLAT
+	depends on FS_ROMFS && BUILD_FLAT && BOARDCTL_ROMDISK
 	---help---
 		This example supports a very, non-standard but also very convenient
 		way of testing with example using CONFIG_EXAMPLES_SOTEST_BUILTINFS.