x86_32, signal: Fix vdso rt_sigreturn

x86_32, signal: Fix vdso rt_sigreturn

This commit:

    commit 6f121e548f83674ab4920a4e60afb58d4f61b829
    Author: Andy Lutomirski <luto@amacapital.net>
    Date:   Mon May 5 12:19:34 2014 -0700

        x86, vdso: Reimplement vdso.so preparation in build-time C

Contained this obvious typo:

-               restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);
+               restorer = current->mm->context.vdso +
+                       selected_vdso32->sym___kernel_sigreturn;

Note the missing 'rt_' in the new code.  Fix it.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/1eb40ad923acde2e18357ef2832867432e70ac42.1403361010.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>