mmc: block: don't use the OR operation for flag of data

After removed the MMC_DATA_STREAM, only two flags are remained.
(MMC_DATA_READ and MMC_DATA_WRITE)
The flags of  READ and WRITE can't be used together.
That's why it doesn't need to use "OR' operation.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>