[40] st/scroll-view-fade: Simplify shader a bit
The shader was using too many ALU instructions for Intel 945GM hardware, so simplify it a bit. The resulting math is the same, but a few redundant operations have been removed.
Fixes: #4883 (closed) Part-of: !2072 (merged)
(cherry picked from commit 7e0c6dc2)
For our Intel 3. gen GPU folks!
Edited by Robert Mader