mmc: sdhi: remove unneeded initialization

Bools are initialized to 'false' by default.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>