mmc: sdhci: use IS_REACHABLE(CONFIG_LEDS_CLASS) to enable LED code

defined(CONFIG_LEDS_CLASS) || (defined(CONFIG_LEDS_CLASS_MODULE) && \
    defined(CONFIG_MMC_SDHCI_MODULE))

is equivalent to:

defined(CONFIG_LEDS_CLASS) || (defined(CONFIG_LEDS_CLASS_MODULE) && \
    defined(MODULE))

and it can also be written shortly as:

IS_REACHABLE(CONFIG_LEDS_CLASS)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>