ath9k: Select RELAY for ATH9K_DEBUGFS

The spectral scan support activated through ATH9K_DEBUGFS depends on RELAY for
the kernel->userspace communication. Not activating RELAY causes build
failures.

The RELAY is added as select instead of depend to do it similar like
the only other user of RELAY: BLK_DEV_IO_TRACE

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>