arm: irq: l2c: do not print error in case of missing l2c from dtb

In some architectures the L2 cache controller is integrated in the
processor's block itself and it doesn't use any external cache
controller. This means that an entry in the board's dtb related
to the l2c is not necessary.

Distinguish between error codes and do not print anything in case
l2x0_of_init() doesn't find any L2C DTB entry and returns -ENODEV.

This patch mutes the following error message:

   L2C: failed to init: -19

on boards like odroid-xu4, cortex A7/A15, which don't have
external cache controller.
Signed-off-by: Andi Shyti <andi.shyti@samsung.com>
Reported-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>