MAINTAINERS: Add FSI subsystem

The subsystem was merged some time ago but we did not have a maintainers
entry. The mailing list exists to allow our patchwork to slurp up the
patches. The tree will be co-maintained by myself and Jeremy.

Acked-by: Jeremy Kerr <[e-mail]>
Signed-off-by: Joel Stanley <[e-mail]>

MAINTAINERS

···
 F:	include/linux/fscrypt*.h
 F:	Documentation/filesystems/fscrypt.rst
 
+FSI SUBSYSTEM
+M:	Jeremy Kerr <[e-mail]>
+M:	Joel Stanley <[e-mail]>
+R:	Alistar Popple <[e-mail]>
+R:	Eddie James <[e-mail]>
+L:	[e-mail]
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/joel/fsi.git
+Q:	http://patchwork.ozlabs.org/project/linux-fsi/list/
+S:	Supported
+F:	drivers/fsi/
+F:	include/linux/fsi*.h
+F:	include/trace/events/fsi*.h
+
 FSI-ATTACHED I2C DRIVER
 M:	Eddie James <[e-mail]>
 L:	[e-mail]