kcov, usb: hide in_serving_softirq checks in __usb_hcd_giveback_urb

Done opencode in_serving_softirq() checks in in_serving_softirq() to avoid
cluttering the code, hide them in kcov helpers instead.

Fixes: aee9ddb1

 ("kcov, usb: only collect coverage from __usb_hcd_giveback_urb in softirq")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://lore.kernel.org/r/aeb430c5bb90b0ccdf1ec302c70831c1a47b9c45.1609876340.git.andreyknvl@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>