mmc: core: Drop retries as in-parameter to mmc_wait_for_app_cmd()

All callers of mmc_wait_for_app_cmd() set the retries in-parameter to
MMC_CMD_RETRIES. This is silly, so let's just drop the in-parameter
altogether, as to simplify the code.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>