x86/entry: spell EBX register correctly in documentation

BugLink: https://bugs.launchpad.net/bugs/1810967

[ Upstream commit 75ca5b22 ]

As EBS does not mean anything reasonable in the context it is used, it
seems like a misspelling for EBX.
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/entry/entry_64.S

@@ -1226,7 +1226,7 @@ END(error_entry)
 
 
 /*
- * On entry, EBS is a "return to kernel mode" flag:
+ * On entry, EBX is a "return to kernel mode" flag:
  *   1: already in kernel mode, don't need SWAPGS
  *   0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode
  */