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: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>