Correct return value of MagnificationController#reset

It only returns true if magnification changes from magnifying to
non-magnifying. This is inconsistent with the docs. Return true if
the magnification scale and center is reset.

Bug: 64616261
Test: atest CtsAccessibilityTestCases
Test: atest CtsAccessibilityServiceTestCases
Change-Id: I0c496c5c45c2e35025f1887842a2a9741c440af1