i2c: aspeed: fix build warning

Upstream commit 3e9efc32 ("i2c: aspeed: Handle master/slave combined irq events
properly") reworked the interrupt handling and fixed a warning in the process:

drivers/i2c/busses/i2c-aspeed.c: In function 'aspeed_i2c_bus_irq':
drivers/i2c/busses/i2c-aspeed.c:567:1: error: label 'out' defined but not used [-Werror=unused-label]

The warning is still present in v4.19.8 and can be fixed either by applying
that original patch, or by adding a simple #ifdef.

Here, I choose the second simpler option as the original patch seems too
invasive for a stable backport.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>