USB: Turn usb_resume_both() into static inline

drivers/usb/core/hub.c: In function `hub_events':
drivers/usb/core/hub.c:2591: warning: statement with no effect

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>