x86/srso: Add a forgotten NOENDBR annotation

Fix:

  vmlinux.o: warning: objtool: .export_symbol+0x29e40: data relocation to !ENDBR: srso_untrain_ret_alias+0x0
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>

arch/x86/lib/retpoline.S

@@ -151,6 +151,7 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array)
 	.section .text.__x86.rethunk_untrain
 
 SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)
+	ANNOTATE_NOENDBR
 	ASM_NOP2
 	lfence
 	jmp __x86_return_thunk