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 <[email protected]>
Cc: Rajeshwari Shinde <[email protected]>
Cc: Jaehoon Chung <[email protected]>
Cc: Mischa Jonker <[email protected]>
Cc: Alexey Brodkin <[email protected]>
Cc: Andy Fleming <[email protected]>
Cc: Pantelis Antoniou <[email protected]>
Acked-by: Pantelis Antoniou <[email protected]>