libgfapi: A minor bug-fix in glfs_h_setxattr and glfs_h_removexattr calls.

Change-Id: I62f63da37edf722d6d79c75f72ee7403e93e4936
BUG: 1089414
Signed-off-by: Soumya Koduri <skoduri@redhat.com>
Reviewed-on: http://review.gluster.org/7529
Reviewed-by: Santosh Pradhan <spradhan@redhat.com>
Tested-by: Meghana M <mmadhusu@redhat.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>