mmc: sdhci-msm: avoid unused function warning

The newly added sdhci_msm_restore_sdr_dll_config() function is only called
if CONFIG_PM is enabled:

drivers/mmc/host/sdhci-msm.c:1050:12: error:
'sdhci_msm_restore_sdr_dll_config' defined but not used
[-Werror=unused-function]

Better remove the incorrect #ifdef altogether and just use __maybe_unused,
which is harder to get wrong.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>