Correct argument order of wm density

Previous change mistakenly thought the arguments are:
 density [-d DISPLAY_ID] [-u UNIQUE_ID] [reset|DENSITY]
But the hint in help info is:
 density [reset|DENSITY] [-d DISPLAY_ID] [-u UNIQUE_ID]

Bug: 186124236
Bug: 355647098
Flag: EXEMPT bugfix
Test: Create a virtual display.
      Change the density of the display:
        adb shell wm density 300 -d 2
        adb shell wm density 300 -u "virtual:a.test,1000,VD,2"
      Print the density of the display
        adb shell wm density -d 2
        adb shell wm density -u "virtual:a.test,1000,VD,2"
Change-Id: Iaa3d0dc45958981d27f2bcdb7c095836ce2fcbe2