The TWL6040 ASoC support has recently started turning on CLK_TWL6040,
but that fails to build when CONFIG_COMMON_CLK is disabled:

warning: (SND_OMAP_SOC_OMAP_ABE_TWL6040) selects CLK_TWL6040 which has unmet direct dependencies (COMMON_CLK && TWL6040_CORE)
0xF18E38F6 Thu Jun 9 18:57:32 CEST 2016 failed
In file included from ../include/linux/clocksource.h:18:0,
                 from ../drivers/clocksource/timer-nps.c:34:
../include/linux/of.h:1005:20: error: comparison of distinct pointer types lacks a cast [-Werror]
        .data = (fn == (fn_type)NULL) ? fn : fn  }
                    ^

This adds a dependency to avoid the invalid configuration.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 443500a3 ("ASoC: omap: Kconfig: SND_OMAP_SOC_OMAP_ABE_TWL6040 to select CLK_TWL6040")
Signed-off-by: Mark Brown <broonie@kernel.org>