mmc: core: Drop redundant bouncesz from struct mmc_card

The commit de3ee99b ("mmc: Delete bounce buffer handling") removed the
bounce buffer handling from the mmc core, but forgot to remove the bouncesz
member from the struct mmc_card, let's fix it.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210202101626.64503-1-ulf.hansson@linaro.org