MAINTAINERS: add entry for ltc1660 DAC driver

Add entry for ltc1660 DAC driver and add myself as
maintainer of this driver.

Signed-off-by: Marcus Folkesson <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

MAINTAINERS

···
 S:	Maintained
 F:	drivers/scsi/sym53c8xx_2/
 
+LTC1660 DAC DRIVER
+M:	Marcus Folkesson <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/dac/ltc1660.txt
+F:	drivers/iio/dac/ltc1660.c
+
 LTC4261 HARDWARE MONITOR DRIVER
 M:	Guenter Roeck <[e-mail]>
 L:	[e-mail]