vlynq: fix typo in Kconfig to enable debugging

Fix a typo in the VLYNQ bus driver Kconfig which prevented to turn on
VLYNQ bus debugging.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>