media: pci/pt1: suppress compiler warning in xtensa arch

Found and reported by kbuild test robot:
Message ID: <201805052003.MC007f9h%fengguang.wu@intel.com>
and holding an address of an empty struct in .driver.pm does no harm
when CONFIG_PM_SLEEP is not defined.

Signed-off-by: Akihiro Tsukada <tskd08@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>