i915/perf: Fix NULL deref bugs with drm_dbg() calls

When i915 perf interface is not available dereferencing it will lead to
NULL dereferences.

As returning -ENOTSUPP is pretty clear return when perf interface is not
available.

Fixes: 2fec5391 ("i915/perf: Replace DRM_DEBUG with driver specific drm_dbg call")
Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v6.0+
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231027172822.2753059-1-harshit.m.mogalapalli@oracle.com
[tursulin: added stable tag]

drivers/gpu/drm/i915/i915_perf.c

@@ -4227,11 +4227,8 @@ int i915_perf_open_ioctl(struct drm_device *dev, void *data,
 	u32 known_open_flags;
 	int ret;
 
-	if (!perf->i915) {
-		drm_dbg(&perf->i915->drm,
-			"i915 perf interface not available for this system\n");
+	if (!perf->i915)
 		return -ENOTSUPP;
-	}
 
 	known_open_flags = I915_PERF_FLAG_FD_CLOEXEC |
 			   I915_PERF_FLAG_FD_NONBLOCK |
@@ -4607,11 +4604,8 @@ int i915_perf_add_config_ioctl(struct drm_device *dev, void *data,
 	struct i915_oa_reg *regs;
 	int err, id;
 
-	if (!perf->i915) {
-		drm_dbg(&perf->i915->drm,
-			"i915 perf interface not available for this system\n");
+	if (!perf->i915)
 		return -ENOTSUPP;
-	}
 
 	if (!perf->metrics_kobj) {
 		drm_dbg(&perf->i915->drm,
@@ -4773,11 +4767,8 @@ int i915_perf_remove_config_ioctl(struct drm_device *dev, void *data,
 	struct i915_oa_config *oa_config;
 	int ret;
 
-	if (!perf->i915) {
-		drm_dbg(&perf->i915->drm,
-			"i915 perf interface not available for this system\n");
+	if (!perf->i915)
 		return -ENOTSUPP;
-	}
 
 	if (i915_perf_stream_paranoid && !perfmon_capable()) {
 		drm_dbg(&perf->i915->drm,