mmc: host: Fix Kconfig warnings on keystone_defconfig

Commit 961de0a8 ("mmc: sdhci-omap: Workaround errata regarding
SDR104/HS200 tuning failures (i929)") added a select on TI_SOC_THERMAL
for the driver to get temperature for tuning.

However, this causes the following warning on keystone_defconfig because
keystone does not support TI_SOC_THERMAL:

"WARNING: unmet direct dependencies detected for TI_SOC_THERMAL"

Fix this by changing the select to imply.

Fixes: 961de0a8 ("mmc: sdhci-omap: Workaround errata regarding
SDR104/HS200 tuning failures (i929)")
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Tested-by: Borislav Petkov <bp@suse.de>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>