greybus: sdio: increase maximum segment size

Adjust maximum segment size of the sg list to meet the maximum request
size, this will allow to have less segments which increase the
performance of data movement during transfer operations.

Test Done: using mmc_test with best-case read/write performance and see
that only one segment is used and that the results are better (288KiB vs
300KiB in read operation).

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