x86: Use tab instead of space to indent in PCIE_ECAM_BASE

Space is used before 'default' in PCIE_ECAM_BASE in arch/x86/Kconfig
so it looks misaligned. Replace the space with tab to indent.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>