staging: fbtft: fix Macros with complex values should be enclosed in parentheses

This patch fixes the following checkpatch.pl error:
fix Macros with complex values should be enclosed in parentheses
Signed-off-by: Heba Aamer <heba93aamer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fb_pcd8544.c

@@ -33,7 +33,7 @@
 #define DRVNAME	       "fb_pcd8544"
 #define WIDTH          84
 #define HEIGHT         48
-#define TXBUFLEN       84*6
+#define TXBUFLEN       (84*6)
 #define DEFAULT_GAMMA  "40" /* gamma is used to control contrast in this driver */
 
 static unsigned tc = 0;