x86: Fix comments of register/stack access functions

Fix typos and some redundant comments of register/stack access
functions in asm/ptrace.h.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Wenji Huang <wenji.huang@oracle.com>
Cc: Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com>
LKML-Reference: <20091201000222.7669.7477.stgit@harusame>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Suggested-by: Wenji Huang <wenji.huang@oracle.com>