drm/amdgpu: Fix realloc of ptr

Clang static analysis reports this error
amdgpu_debugfs.c:1690:9: warning: 1st function call
  argument is an uninitialized value
  tmp = krealloc_array(tmp, i + 1,
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~

realloc uses tmp, so tmp can not be garbage.
And the return needs to be checked.

Fixes: 5ce5a584 ("drm/amdgpu: add debugfs for reset registers list")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1678,7 +1678,7 @@ static ssize_t amdgpu_reset_dump_register_list_write(struct file *f,
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)file_inode(f)->i_private;
 	char reg_offset[11];
-	uint32_t *tmp;
+	uint32_t *new, *tmp = NULL;
 	int ret, i = 0, len = 0;
 
 	do {
@@ -1689,7 +1689,12 @@ static ssize_t amdgpu_reset_dump_register_list_write(struct file *f,
 			goto error_free;
 		}
 
-		tmp = krealloc_array(tmp, i + 1, sizeof(uint32_t), GFP_KERNEL);
+		new = krealloc_array(tmp, i + 1, sizeof(uint32_t), GFP_KERNEL);
+		if (!new) {
+			ret = -ENOMEM;
+			goto error_free;
+		}
+		tmp = new;
 		if (sscanf(reg_offset, "%X %n", &tmp[i], &ret) != 1) {
 			ret = -EINVAL;
 			goto error_free;