dict: Remove the redundant hash calculation when the hash size is 1

Currently the dict is created with hash size 1, i.e. there is
only one hash bucket and the calculation of hash decomes redundant.

Change-Id: Id70aea0d798902494ebb6d82955d97d591bc73d2
BUG: 789278
Signed-off-by: Poornima Gurusiddaiah <pgurusid@redhat.com>
Reviewed-on: http://review.gluster.org/8211
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra Talur <rtalur@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>