soc/intel/quark/spi: Correct conversion specifier

Use the correct conversion specifier for `size_t` to fix the error
below.

```
from src/soc/intel/quark/spi.c:18:
src/soc/intel/quark/spi.c: In function 'xfer':
src/soc/intel/quark/spi.c:107:20: error: format '%ld' expects argument \
   of type 'long int', but argument 3 has type 'unsigned int' \
   [-Werror=format=]
   printk(BIOS_ERR, "bytesin > %ld\n", sizeof(ctrlr->data));
                    ^
```

Found-by: gcc (Debian 7.2.0-8) 7.2.0
Change-Id: I3974d116e85715086a2bd5533a80a20c4cc43303
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: https://review.coreboot.org/22130
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/intel/quark/spi.c

@@ -104,7 +104,7 @@ static int xfer(const struct spi_slave *slave, const void *dout,
 
 	/* Validate the buffer sizes */
 	if (bytesin > sizeof(ctrlr->data)) {
-		printk(BIOS_ERR, "bytesin > %ld\n", sizeof(ctrlr->data));
+		printk(BIOS_ERR, "bytesin > %zu\n", sizeof(ctrlr->data));
 		goto error;
 	}