gluster: fix create volume brick validation

While creating a Striped-Replicated volume, the code which
validates the number of bricks is missing 'break' in a swith-case.
This is now fixed.

Change-Id: I16a5b93f687f5411c08a59804d731d7f4644b12b
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>