Fix Storwize/SVC LUN allocation with holes.

The Storwize/SVC driver should find the first unused LUN, but
continues searching, returning erroneous results.  Added 'break'
statement to fix.

Change-Id: Ibd95714e086a513a39fe9d20ffec57135dc5ec55
Fixes: bug 1157012
Merge "Fix Storwize/SVC LUN allocation with holes."