Mention userId when using WallpaperManager#getWallpaperColors in DesktopWallpaperActivity

DesktopWallpaperActivity runs on user 0 which gives incorrect wallpaper
colors for HSUM user 10

Test: mp droid and locally tested status bar icons are in correct color in desktop mode. Also tested wallpaper change. Tested on both HSUM and non-HSUM
Flag: com.android.window.flags.enable_desktop_windowing_wallpaper_activity
Bug: 415332896
Change-Id: I4ce264f491086280e53fce36792f4ca066aea43e