x86/bugs: Correct RSB terminology in Kconfig

x86/bugs: Correct RSB terminology in Kconfig

RSB stands for "Return Stack Buffer" in industry literature[1]. Update
the kernel Kconfig to use this standard term instead of the current
"Return-Speculation-Buffer".

This change aligns kernel documentation with widely accepted terminology.

The line length reduction triggers text reformatting, but no functional
text is altered.

[1] https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/return-stack-buffer-underflow.html

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20240913122754.249306-1-leitao%40debian.org