x86/sgx: Correct kernel-doc's arg name in sgx_encl_release()

Fix the following kernel-doc warning:

  arch/x86/kernel/cpu/sgx/encl.c:392: warning: Function parameter \
    or member 'ref' not described in 'sgx_encl_release'

 [ bp: Massage commit message. ]

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210609035510.2083694-1-chenxiaosong2@huawei.com