SF: fixing typo

This is in theory a no-op change since the chances of dpiX == -1 && dpiY
!= -1 are virtually null. But for correctedness might be good to clean
up.

Flag: com.android.graphics.surfaceflinger.flags.correct_dpi_with_display_size
Bug: 361413340
Test: HWComposerTest
Change-Id: I967edcf86f92b94db7b861129ab788567c133618