spi: atcspi200: Fix compiler warning

Fix warning as below when compile in 64-bit.

warning: format '%u' expects argument of type
'unsigned int', but argument 6 has type 'size_t
{aka long unsigned int}

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Cc: Greentime Hu <green.hu@gmail.com>