staging: fbtft: remove redundant initialization of buf

The pointer buf is being set on each iteration of a for-loop and
so the initialization of buf at declaration time is redundant and
can be removed.  Cleans up clang warning:

drivers/staging/fbtft/fb_uc1701.c:130:6: warning: Value stored to 'buf' during its initialization is never read
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fb_uc1701.c

@@ -127,7 +127,7 @@ static void set_addr_win(struct fbtft_par *par, int xs, int ys, int xe, int ye)
 static int write_vmem(struct fbtft_par *par, size_t offset, size_t len)
 {
 	u16 *vmem16 = (u16 *)par->info->screen_buffer;
-	u8 *buf = par->txbuf.buf;
+	u8 *buf;
 	int x, y, i;
 	int ret = 0;