As part of renaming environment related Kconfig options,
ENV_MMC_SW_PARTITION was inadvertently changed from a string to a bool.
Correct this.
Fixes: ffc4914703a2 ("env: Rename ENV_MMC_PARTITION to ENV_MMC_SW_PARTITION")
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Signed-off-by: Tom Rini <trini@konsulko.com>