PCI/sysfs: Add 'devspec' newline

Previously, when the value of the "devspec" sysfs attribute was read from
the user space there was no newline present, and utilities such as "cat"
wouldn't display the result of the read correctly.

Append a newline character in the show() function to match other "devspec"
attributes.

Link: https://lore.kernel.org/r/20210603000112.703037-5-kw@linux.com


Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>