usb: host: oxu210hp-hcd: Move declaration of 'qtd' into 'ifdef OXU_URB_TRACE'

usb: host: oxu210hp-hcd: Move declaration of 'qtd' into 'ifdef OXU_URB_TRACE'

If we assign 'epnum' during the declaration we can also avoid "ISO
C90 forbids mixed declarations" issues.  So it does looks like we
can have our cake and eat it in this scenario.

Fixes the following W=1 kernel build warning(s):

 drivers/usb/host/oxu210hp-hcd.c: In function ‘submit_async’:
 drivers/usb/host/oxu210hp-hcd.c:2040:19: warning: variable ‘qtd’ set but not used [-Wunused-but-set-variable]
 2040 | struct ehci_qtd *qtd;
 | ^~~

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Rodolfo Giometti <giometti@linux.it>
Cc: "Eurotech S.p.A" <info@eurtech.it>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200702144625.2533530-24-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>