The dw_mci_init_dma() may decide to not use dma, but pio instead, caused
by things like wrong dma settings in the system.

Till now the code dw_mci_init_slot() always assumed that dma is available
when CONFIG_MMC_DW_IDMAC was defined, ignoring the host->use_dma var
set during dma init.

So when now the dma init failed for whatever reason, the transfer sizes
would still be set for dma transfers, especially including the maximum
block-count calculated from host->ring_size and resulting in a

[    4.991109] ------------[ cut here ]------------
[    4.991111] kernel BUG at drivers/mmc/core/core.c:256!
[    4.991113] Internal error: Oops - BUG: 0 [#1] SMP ARM

because host->ring_size is 0 in this case and the slot init code uses
the wrong code to calculate the values.

Fix this by selecting the correct calculations using the host->use_dma
variable instead of the CONFIG_MMC_DW_IDMAC config option.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>