drm/mipi_dbi: Use simple right shift instead of double negation

GCC complains about dubious bitwise OR operand:

drivers/gpu/drm/drm_mipi_dbi.c:1024:49: warning: dubious: x | !y
  CC [M]  drivers/gpu/drm/drm_mipi_dbi.o

As long as buffer is consist of byte (u8) values, we may use
simple right shift and satisfy compiler. It also reduces amount of
operations needed.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191017114912.61522-1-andriy.shevchenko@linux.intel.com

drivers/gpu/drm/drm_mipi_dbi.c

@@ -1021,7 +1021,7 @@ static int mipi_dbi_typec3_command_read(struct mipi_dbi *dbi, u8 *cmd,
 		unsigned int i;
 
 		for (i = 0; i < len; i++)
-			data[i] = (buf[i] << 1) | !!(buf[i + 1] & BIT(7));
+			data[i] = (buf[i] << 1) | (buf[i + 1] >> 7);
 	}
 
 	MIPI_DBI_DEBUG_COMMAND(*cmd, data, len);