pci: Remove unnecessary 'default n' from Kconfig

'default n' is the default anyway so it doesn't need to be specified
explicitly, and the rest of the file doesn't specify it either anywhere.
Drop it.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>