Clang detected a problem with rc possibly being unitialized
(when length is zero) in a recently added fallocate code path.
Reported-by: Nkernel test robot <lkp@intel.com>
Reviewed-by: NPaulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: NSteve French <stfrench@microsoft.com>