usb: device: nrf5: Fix HF clock enable check

Fixed return value check after HF clock is requested in
non-blocking mode.

hci_usb sample on nRF52840 SoC failed to enumerate USB
device on cold reset, the clock_control_on interface would
return -EINPROGRESS when clock is enabled in non-blocking
mode.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>