staging: wfx: drop useless check

Currently, the ISR check if bus->core is not NULL. But, it is a useless
check. bus->core is initialiased before to request IRQ and it is not
assigned to NULL when it is released.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200505123757.39506-5-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>