drm/amdgpu/debugfs: fix error code when smc register accessors are NULL

jira LE-3201
cve CVE-2023-52817
Rebuild_History Non-Buildable kernel-rt-4.18.0-553.22.1.rt7.363.el8_10
commit-author Alex Deucher <alexander.deucher@amd.com>
commit afe5834

Should be -EOPNOTSUPP.

Fixes: 5104fdf ("drm/amdgpu: Fix a null pointer access when the smc_rreg pointer is NULL")
	Reviewed-by: Christian König <christian.koenig@amd.com>
	Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit afe5834)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

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

@@ -590,7 +590,7 @@ static ssize_t amdgpu_debugfs_regs_smc_read(struct file *f, char __user *buf,
 	int r;
 
 	if (!adev->smc_rreg)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	if (size & 0x3 || *pos & 0x3)
 		return -EINVAL;
@@ -649,7 +649,7 @@ static ssize_t amdgpu_debugfs_regs_smc_write(struct file *f, const char __user *
 	int r;
 
 	if (!adev->smc_wreg)
-		return -EPERM;
+		return -EOPNOTSUPP;
 
 	if (size & 0x3 || *pos & 0x3)
 		return -EINVAL;