docs: Fixing malformatted HTML escape

Through the file's javadoc comments, the less-than character is
improperly coded as "&lt" instead of "<" (it's missing the
terminating semicolon). Chrome is clever enough to render that as <
, but I don't know if other browsers do, and in any event we
shouldn't count on that behavior.

Doc is staged to:

http://go/dac-stage/reference/android/graphics/drawable/RippleDrawable.html

Test: make ds-docs
Bug: 62028102
Change-Id: I81813fcb758349300f56ce10ccb0d03046ab4736