ASoC: sgtl5000: Print revision number in hex

Throughout the sgtl5000 driver source code and also in the sgtl5000 datasheet
the revision code is shown in hexadecimal.

Print it hex format, for consistency.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>