Add include to i2c-xii.c to fix build error

drivers/i2c/busses/i2c-xiic.c:493: error: implicit declaration of function 'mdelay'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: "Richard Röjfors" <richard.rojfors@pelagicore.com>
Cc: "Ben Dooks (embedded platforms)" <ben-linux@fluff.org>
Cc: linux-i2c@vger.kernel.org
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>