ASoC: rcar: dma: remove unnecessary "volatile"

commit 2a3af642eb20("ASoC: rcar: clear DE bit only in PDMACHCR...")
added rsnd_dmapp_bset(), but it used copy-paste. Thus, it had
unnecessary "volatile", and had below warning on x86.
This patch fix it.

   sound/soc/sh/rcar/dma.c: In function 'rsnd_dmapp_bset':
>> sound/soc/sh/rcar/dma.c:463:21: warning: passing argument 1 of \
   'ioread32' discards 'volatile' qualifier from pointer target \
   type [-Wdiscarded-qualifiers]
     u32 val = ioread32(addr);
                        ^~~~
   In file included from arch/x86/include/asm/io.h:203:0,
                    from arch/x86/include/asm/realmode.h:5,
                    from arch/x86/include/asm/acpi.h:33,
                    from arch/x86/include/asm/fixmap.h:19,
                    from arch/x86/include/asm/apic.h:10,
                    from arch/x86/include/asm/smp.h:12,
                    from include/linux/smp.h:59,
                    from include/linux/topology.h:33,
                    from include/linux/gfp.h:8,
                    from include/linux/idr.h:16,
                    from include/linux/kernfs.h:14,
                    from include/linux/sysfs.h:15,
                    from include/linux/kobject.h:21,
                    from include/linux/of.h:21,
                    from include/linux/of_dma.h:16,
                    from sound/soc/sh/rcar/dma.c:12:
   include/asm-generic/iomap.h:31:21: note: expected 'void *' \
   but argument is of type 'volatile void *'
    extern unsigned int ioread32(void __iomem *);
                        ^~~~~~~~
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>