tty: serial: pmac_zilog: Remove unused disposable variable 'garbage'

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

 drivers/tty/serial/pmac_zilog.h:365:58: warning: variable ‘garbage’ set but not used [-Wunused-but-set-variable]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linux-serial@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112105857.2078977-5-lee.jones@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>