usb: host: r8a66597-hcd: Remove set, then over-written, but never used variable ...

usb: host: r8a66597-hcd: Remove set, then over-written, but never used variable 'tmp'

Looks like it's been this way since the driver's inception in 2007.

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

 drivers/usb/host/r8a66597-hcd.c: In function ‘clear_all_buffer’:
 drivers/usb/host/r8a66597-hcd.c:478:6: warning: variable ‘tmp’ set but not used [-Wunused-but-set-variable]
 478 | u16 tmp;
 | ^~~

Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200706133341.476881-14-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>