usb: gadget: s3c2410_udc: don't use pr_debug return value

pr_debug() may be defined as "do { } while (0)" in some configurations,
which means one cannot rely on the return value to be available.

In the dprintk function in this driver, we can work around the
resulting build error trivially by returning the length that
this function already knows and ignoring the return value of
pr_debug.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: linux-samsung-soc@vger.kernel.org
Signed-off-by: Felipe Balbi <balbi@ti.com>