x86/32: Simplify ELF_CORE_COPY_REGS

GS is now always a user segment, so there is no difference between user
and kernel registers.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20220325153953.162643-2-brgerst@gmail.com