[MLlib] Squash bug in IndexedRowMatrix

Kill this bug fast before it does damage.

Author: Reza Zadeh <rizlar@gmail.com>

Closes #2224 from rezazadeh/indexrmbug and squashes the following commits:

53386d6 [Reza Zadeh] Squash bug in IndexedRowMatrix

mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/IndexedRowMatrix.scala

@@ -130,7 +130,7 @@ class IndexedRowMatrix(
     val indexedRows = rows.map(_.index).zip(mat.rows).map { case (i, v) =>
       IndexedRow(i, v)
     }
-    new IndexedRowMatrix(indexedRows, nRows, nCols)
+    new IndexedRowMatrix(indexedRows, nRows, B.numCols)
   }
 
   /**