irqchip: crossbar: Fix kerneldoc warning

irqchip: crossbar: Fix kerneldoc warning

Adding missing properties for kerneldoc (@write) and cleanup
of harmless warnings while we are here.

kerneldoc warnings:
Warning(drivers/irqchip/irq-crossbar.c:27): missing initial short description on line:
 * struct crossbar_device: crossbar device description
Info(drivers/irqchip/irq-crossbar.c:27): Scanning doc for struct
Warning(drivers/irqchip/irq-crossbar.c:39): No description found for parameter 'write'
2 warnings

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Sricharan R <r.sricharan@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Link: https://lkml.kernel.org/r/1403766634-18543-9-git-send-email-r.sricharan@ti.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>