PCI Hotplug: cpqhp_pushbutton_thread(): remove a pointless if() check

The Coverity checker spotted that we'd have already oops'ed if "ctrl"
was NULL.

Additionally, "func" had just been checked for not being NULL.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>