[SPARK-38816][ML][DOCS] Fix comment about choice of initial factors in ALS

### What changes were proposed in this pull request?

Change a comment in ALS code to match impl. The comment refers to taking the absolute value of a Normal(0,1) value, but it doesn't.

### Why are the changes needed?

The docs and impl are inconsistent. The current behavior actually seems fine, desirable, so, change the comments.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Existing tests

Closes apache#36228 from srowen/SPARK-38816.

Authored-by: Sean Owen <srowen@gmail.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: srowen

mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala

@@ -1279,9 +1279,8 @@ object ALS extends DefaultParamsReadable[ALS] with Logging {
       inBlocks: RDD[(Int, InBlock[ID])],
       rank: Int,
       seed: Long): RDD[(Int, FactorBlock)] = {
-    // Choose a unit vector uniformly at random from the unit sphere, but from the
-    // "first quadrant" where all elements are nonnegative. This can be done by choosing
-    // elements distributed as Normal(0,1) and taking the absolute value, and then normalizing.
+    // Choose a unit vector uniformly at random from the unit sphere. This can be done by choosing
+    // elements distributed as Normal(0,1), and then normalizing.
     // This appears to create factorizations that have a slightly better reconstruction
     // (<1%) compared picking elements uniformly at random in [0,1].
     inBlocks.mapPartitions({ iter =>