ceph: correct comment to match striping calculation
ceph: correct comment to match striping calculation

The object extent offset is the file offset _modulo_ the stripe unit.
The code was correct, the comment was wrong.

Reported-by: Noah Watkins <a4e8cabdfba647fc9c917931c003046bb6bb0102@soe.ucsc.edu>
Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

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