env_mmc: correct fini partition to match init partition

The code to set the MMC partition uses an weak function to obtain the
correct partition number.  Use that instead of the compile-time default
when deciding whether it needs to switch back.

Fixes: 6e7b7df4df43574 ("env_mmc: support env partition setup in runtime")
Signed-off-by: Peter A. Bigot <pab@pabigot.com>
Acked-by: Dmitry Lifshitz <lifshitz@compulab.co.il>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>

common/env_mmc.c

@@ -113,7 +113,7 @@ static void fini_mmc_for_env(struct mmc *mmc)
 #ifdef CONFIG_SPL_BUILD
 	dev = 0;
 #endif
-	if (CONFIG_SYS_MMC_ENV_PART != mmc->part_num)
+	if (mmc_get_env_part(mmc) != mmc->part_num)
 		mmc_switch_part(dev, mmc->part_num);
 #endif
 }