wlcore: Always pass DMA-able buffers to mmc functions

Some of the mmc drivers initiate DMA transfers with buffers passed from
higher layers. This means that the driver shouldn't ever pass non
DMA-able buffers, such as ones that are unaligned, allocated on the
stack or static.

Fix a couple of calls to the mmc layer in which buffers which weren't
necessarily DMA-able were passed.

[Use sizeof(*wl->buffer_32) instead of sizeof(u32) -- Luca]

Signed-off-by: Ido Yariv <ido@wizery.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>