apps/nshlib: allow use of read-only romfs image

Change-Id: Iaedf68dbccd19d55b5927a19d07abf42bb743992
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@haltian.com>
(cherry picked from commit c0bce7d9c9d4dabbf43aafe340da387a068595d1)

apps/nshlib/nsh_romfsetc.c

@@ -99,7 +99,7 @@ int nsh_romfsetc(void)
 
   /* Create a ROM disk for the /etc filesystem */
 
-  ret = romdisk_register(CONFIG_NSH_ROMFSDEVNO, romfs_img,
+  ret = romdisk_register(CONFIG_NSH_ROMFSDEVNO, (void*)romfs_img,
                          NSECTORS(romfs_img_len), CONFIG_NSH_ROMFSSECTSIZE);
   if (ret < 0)
     {