irqchip: gic-v3-its: Fix use of max with decimal constant

arm64 defconfig spits out the following compiler warning from the ITS
driver:

In file included from include/linux/bitmap.h:9:0,
                 from drivers/irqchip/irq-gic-v3-its.c:18:
drivers/irqchip/irq-gic-v3-its.c: In function ‘its_create_device’:
include/linux/kernel.h:716:17: warning: comparison of distinct pointer types lacks a cast
  (void) (&_max1 == &_max2);  \
                 ^
drivers/irqchip/irq-gic-v3-its.c:1056:12: note: in expansion of macro ‘max’
  nr_ites = max(2, roundup_pow_of_two(nvecs));

Fix the warning by specifying the decimal constant `2' explicitly as an
unsigned long type.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1418825469-30529-1-git-send-email-will.deacon@arm.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>