mmc/dwmmc: Using calloc instead malloc

mmc/dwmmc: Using calloc instead malloc

To enhance the SDMMC DesignWare driver to use calloc instead of
malloc. This will avoid the incident that uninitialized members
of mmc structure are later used for NULL comparison.

Signed-off-by: Chin Liang See <clsee@altera.com>
Cc: Rajeshwari Shinde <rajeshwari.s@samsung.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Mischa Jonker <mjonker@synopsys.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Andy Fleming <afleming@freescale.com>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>