cli_classic.c: Use correct format specifier for size_t

The return value of `flashrom_flash_getsize()` is of `size_t` type.

Fixes: commit 83c5c50f91
Change-Id: I8025c0e046cb61e0e115d3786e6e4184190347f1
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/62707
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>

cli_classic.c

@@ -715,7 +715,7 @@ int main(int argc, char *argv[])
 	}
 
 	if (flash_size) {
-		printf("%ld\n", flashrom_flash_getsize(fill_flash));
+		printf("%zu\n", flashrom_flash_getsize(fill_flash));
 		goto out_shutdown;
 	}