Don't reassign `desiredAspectRatio` parameter in`applyAspectRatio`

`ActivityRecord.applyAspectRatio` receives `desiredAspectRatio` as an
input parameter but reassigns it values multiple times within the
method. To remove the input parameter reassignment and preserve the
original value of `desiredAspectRatio`, replace its use with a local
variable which will be assigned the value of `desiredAspectRatio` at
the start.

Fix: 287239360
Test: atest WmTests:ActivityRecordTest
Change-Id: Ib78886883fe848d680adb9fcfe484097453e1eae