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>
diff --git a/drivers/tty/serial/pmac_zilog.h b/drivers/tty/serial/pmac_zilog.h
index bb874e7..fa85b0d 100644
--- a/drivers/tty/serial/pmac_zilog.h
+++ b/drivers/tty/serial/pmac_zilog.h
@@ -362,10 +362,10 @@ static inline void zssync(struct uart_pmac_port *port)
 
 /* Misc macros */
 #define ZS_CLEARERR(port)    (write_zsreg(port, 0, ERR_RES))
-#define ZS_CLEARFIFO(port)   do { volatile unsigned char garbage; \
-				     garbage = read_zsdata(port); \
-				     garbage = read_zsdata(port); \
-				     garbage = read_zsdata(port); \
+#define ZS_CLEARFIFO(port)   do {                       \
+				     read_zsdata(port); \
+				     read_zsdata(port); \
+				     read_zsdata(port); \
 				} while(0)
 
 #define ZS_IS_CONS(UP)			((UP)->flags & PMACZILOG_FLAG_IS_CONS)