drivers/spi/spi-s3c64xx.c:387:34: sparse: sparse: Using plain integer as NULL pointer

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   74cae210a335d159f2eb822e261adee905b6951a
commit: 82295bc0d192d7e35e0568b18ca66da2c3058fd5 spi: s3c64xx: move dma_release_channel to unprepare
date:   6 weeks ago
config: arm64-randconfig-s052-20220804 (https://download.01.org/0day-ci/archive/20220806/202208060820.GKre8FkO-lkp@xxxxxxxxx/config)
compiler: aarch64-linux-gcc (GCC) 12.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.4-39-gce1a6720-dirty
        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=82295bc0d192d7e35e0568b18ca66da2c3058fd5
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout 82295bc0d192d7e35e0568b18ca66da2c3058fd5
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=arm64 SHELL=/bin/bash drivers/block/null_blk/./ drivers/spi/ fs/zonefs/./

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@xxxxxxxxx>

sparse warnings: (new ones prefixed by >>)
>> drivers/spi/spi-s3c64xx.c:387:34: sparse: sparse: Using plain integer as NULL pointer
   drivers/spi/spi-s3c64xx.c:388:34: sparse: sparse: Using plain integer as NULL pointer

vim +387 drivers/spi/spi-s3c64xx.c

   375	
   376	static int s3c64xx_spi_unprepare_transfer(struct spi_master *spi)
   377	{
   378		struct s3c64xx_spi_driver_data *sdd = spi_master_get_devdata(spi);
   379	
   380		if (is_polling(sdd))
   381			return 0;
   382	
   383		/* Releases DMA channels if they are allocated */
   384		if (sdd->rx_dma.ch && sdd->tx_dma.ch) {
   385			dma_release_channel(sdd->rx_dma.ch);
   386			dma_release_channel(sdd->tx_dma.ch);
 > 387			sdd->rx_dma.ch = 0;
   388			sdd->tx_dma.ch = 0;
   389		}
   390	
   391		return 0;
   392	}
   393	

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