PCI: endpoint: Fix Kconfig indent style

Change to follow the Kconfig style guide. This patch fixes to use tab
rather than space to indent, while help text is indented an additional
two spaces.

Link: https://lore.kernel.org/r/20220815025006.48167-1-mie@igel.co.jp
Fixes: e35f56bb ("PCI: endpoint: Support NTB transfer between RC and EP")
Signed-off-by: NShunsuke Mie <mie@igel.co.jp>
Signed-off-by: NLorenzo Pieralisi <lpieralisi@kernel.org>