misc: hisi_hikey_usb: Use str_enabled_disabled() in hub_power_ctrl()

misc: hisi_hikey_usb: Use str_enabled_disabled() in hub_power_ctrl()

Remove hard-coded strings by using the str_enabled_disabled() helper
function and silence the following Coccinelle/coccicheck warning
reported by string_choices.cocci:

  opportunity for str_enabled_disabled(value)

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/r/20250813180108.209096-2-thorsten.blum@linux.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>