UBIFS: allow for sync_fs when read-only
UBIFS: allow for sync_fs when read-only

sync_fs can be called even if the file system is mounted
read-only.  Ensure the commit is not run in that case.

Reported-by: Zoltan Sogor <8f92539cee582ffc213cdcceffd2c5c17d819c5a@inf.u-szeged.hu>
Signed-off-by: Adrian Hunter <07e5499f8ca7b9f9593b4a7656ea8c5a05a8f7f6@nokia.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs