lsm: Fix description of fs_context_parse_param

The fs_context_parse_param hook already has a description, which seems the
right one according to the code.

Fixes: 8eb687bc

 ("lsm: Add/fix return values in lsm_hooks.h and fix formatting")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>