soc: aspeed: Add NULL check in aspeed_lpc_enable_snoop()

In the Linux kernel, the following vulnerability has been resolved:

soc: aspeed: Add NULL check in aspeed_lpc_enable_snoop()

devm_kasprintf() returns NULL when memory allocation fails. Currently,

aspeed_lpc_enable_snoop() does not check for this case, which results in a

NULL pointer dereference.

Add NULL check after devm_kasprintf() to prevent this issue.

[arj: Fix Fixes: tag to use subject from 3772e5da4454]