UPSTREAM: usb: dwc2: add printf attribute to cat_printf()

UPSTREAM: usb: dwc2: add printf attribute to cat_printf()

As cat_printf() uses printf format strings in its parameters, adding
__printf attribute allows the compiler to detect at compile-time some
errors related to format strings (with -Wformat warning flag).

Change-Id: I3558d4a331acdf057c1daccbe86008ae0fd07216
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Huang, Tao <huangtao@rock-chips.com>
(cherry picked from commit e135ab7405f562c7709806e355b1521ee68548dc)