mmc: renesas_sdhi: fix WP detection

Commit "mmc: renesas_sdhi: use MMC_CAP2_NO_WRITE_PROTECT instead of
TMIO own flag" activated MMC_CAP2_NO_WRITE_PROTECT for Renesas SDHI
which incorrectly disabled WP altogether instead of only disabling the
internal mechanism. Since the whole WP handling has been reworked, we
can simply disable this capability to re-enable WP GPIOs.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>