mmc: tmio: remove useless TMIO_MASK_CMD handling in tmio_mmc_host_probe()

TMIO_MASK_CMD is properly enabled in tmio_mmc_start_command().

We have no reason to set it up in tmio_mmc_host_probe().  (If we
really wanted to set it in the probe, we would have to do likewise
when resuming.)

Even worse, the following code is extremely confusing:

  _host->sdcard_irq_mask &= ~irq_mask;

The logic is opposite between "->sdcard_irq_mask" and "irq_mask".
The intention is not clear at a glance.

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