greybus: sdio: fix transfer buffer handling and blocks counting

Fix copy to/from scatterlist destination buffer offset, fix
calculation of blocks to be transfer and make a more verbose out of
error when the blocks receive/send do not match.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>