ASoC: remove one extraneous 'const'

A recent commit made a few arrays 'const', but also added the
same attribute to a function return type, where it makes no
sense, and we get a warning when building with W=1:

sound/soc/codecs/arizona.c:1725:27: error: type qualifiers ignored on function return type [-Werror=ignored-qualifiers]
 static const char * const arizona_dai_clk_str(int clk_id)

This removes it again.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>