MAINTAINERS: addition of Dialog Semiconductor files

Dialog Semiconductor Ltd would like to add a new section called DIALOG
SEMICONDUCTOR DRIVERS which contains a new e-mail address that can cover
all Dialog supported drivers: support.opensource@diasemi.com.

Signed-off-by: Opensource [Steve Twiss] <stwiss.opensource@diasemi.com>
Signed-off-by: David Dajun Chen <david.chen@diasemi.com>
Cc: Mark Brown <broonie@linaro.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>