nfsd4: minor read_buf cleanup
nfsd4: minor read_buf cleanup

The code to step to the next page seems reasonably self-contained.

Signed-off-by: J. Bruce Fields <51738506c1b2ccb0761f23bdc612c93babf738ea@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs