crypto: iaa - Fix out-of-bounds index in find_empty_iaa_compression_mode

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

crypto: iaa - Fix out-of-bounds index in find_empty_iaa_compression_mode

The local variable 'i' is initialized with -EINVAL, but the for loop immediately overwrites it and -EINVAL is never returned.

If no empty compression mode can be found, the function would return the out-of-bounds index IAA_COMP_MODES_MAX, which would cause an invalid array access in add_iaa_compression_mode().

Fix both issues by returning either a valid index or -EINVAL.