soc: qcom: llcc: make irq truly optional

The function platform_get_irq prints an error message into the kernel
log when the irq isn't found.

Since the interrupt is actually optional and not provided by some SoCs,
use platform_get_irq_optional which does not print an error message.

Fixes: c081f306 ("soc: qcom: Add support to register LLCC EDAC driver")
Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221104153041.412020-1-luca.weiss@fairphone.com