Fix the following coccicheck warning:
  drivers/memory/tegra/tegra30-emc.c:1322:0-23:WARNING:
    tegra_emc_debug_max_rate_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE
Signed-off-by: jing yangyang <jing.yangyang@zte.com.cn>
Link: https://lore.kernel.org/r/20210821035223.28282-1-jing.yangyang@zte.com.cnSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>