libhwc2.1: Allow display logging from const methods

The DISPLAY_LOGE macro is using the saveErrorLog function, which takes
a non-const ExynosDisplay parameter, which make it impossible to use
this macro in const methods. The logging actually doesn't change the
object state, so we can mark the ExynosDisplay parameter as const.

Bug: 299682821
Test: presubmit
Change-Id: Id341325b2d6ccb42257166612531e581e0b2c10d
3 files changed