return same error value from spk_set_key_info

This patch makes spk_set_key_info return -EINVAL
in case of failure instead of returning 4 different
values for the type of error that occurred.

Print the offending values instead as debug message.

Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>