drm/amdgpu: Mark mmhub_v1_8_mmea_err_status_reg as __maybe_unused

Silencing the compiler from below compilation error:

drivers/gpu/drm/amd/amdgpu/mmhub_v1_8.c:704:23: error: variable 'mmhub_v1_8_mmea_err_status_reg' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
static const uint32_t mmhub_v1_8_mmea_err_status_reg[] = {
^
1 error generated.

Mark the variable as __maybe_unused to make it clear to clang that this
is expected, so there is no more warning.

Cc: Christian König <[e-mail]>
Cc: Lijo Lazar <[e-mail]>
Cc: Luben Tuikov <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Signed-off-by: Srinivasan Shanmugam <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/mmhub_v1_8.c

···
 		mmhub_v1_8_inst_reset_ras_error_count(adev, i);
 }
 
-static const uint32_t mmhub_v1_8_mmea_err_status_reg[] = {
+static const u32 mmhub_v1_8_mmea_err_status_reg[] __maybe_unused = {
 	regMMEA0_ERR_STATUS,
 	regMMEA1_ERR_STATUS,
 	regMMEA2_ERR_STATUS,