gpu: drm: replace occurrences of invalid character

There are some places at drm that ended receiving a
REPLACEMENT CHARACTER U+fffd ('�'), probably because of
some bad charset conversion.

Fix them by using what it seems	to be the proper
character.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e606930c73029f16673849c57acac061dd923866.1621412009.git.mchehab+huawei@kernel.org