drm/amdgpu: Fix out-of-bounds read of df_v1_7_channel_number

Check the fb_channel_number range to avoid the array out-of-bounds
read error

Signed-off-by: Ma Jun <[e-mail]>
Reviewed-by: Tim Huang <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/df_v1_7.c

···
 	int fb_channel_number;
 
 	fb_channel_number = adev->df.funcs->get_fb_channel_number(adev);
+	if (fb_channel_number >= ARRAY_SIZE(df_v1_7_channel_number))
+		fb_channel_number = 0;
 
 	return df_v1_7_channel_number[fb_channel_number];
 }