staging: fbtft: Remove do {} while(0) in single statement macro

This patch fixes the checkpatch.pl warning:

WARNING: Single statement macros should not use a do {} while (0) loop
+#define write_reg(par, ...)                                              \
+do {                                                                     \
+       par->fbtftops.write_register(par, NUMARGS(__VA_ARGS__), __VA_ARGS__); \
+} while (0)

Signed-off-by: Helen Fornazier <helen.fornazier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>