'ret' hasn't  been checked since the driver's inception in 2009.

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

 drivers/usb/early/ehci-dbgp.c: In function ‘early_dbgp_write’:
 drivers/usb/early/ehci-dbgp.c:915:13: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]
 915 | int chunk, ret;
 | ^~~

Cc: Sumit Garg <sumit.garg@linaro.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Link: https://lore.kernel.org/r/20200706133341.476881-26-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>