x86/kaiser: fix build error with KASAN && !FUNCTION_GRAPH_TRACER

This is a build fix for the 4.4 PTI backport.  4.4 kernels do not have
commit be7635e7 ("arch, ftrace: for KASAN put hard/soft IRQ entries
into separate sections") which went into 4.6.  Consequently, the
irqentry sections are only created when CONFIG_FUNCTION_GRAPH_TRACER is
enabled, not also when CONFIG_KASAN is enabled.  Therefore, fix the
condition for trying to add a user mapping for this section.

This fixes the following build error:

    arch/x86/mm/kaiser.c: In function ‘kaiser_init’:
    arch/x86/mm/kaiser.c:367:33: error: ‘__irqentry_text_start’ undeclared (first use in this function)
      kaiser_add_user_map_ptrs_early(__irqentry_text_start,
    [...]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/mm/kaiser.c

@@ -363,7 +363,7 @@ void __init kaiser_init(void)
 	kaiser_add_user_map_ptrs_early(__entry_text_start, __entry_text_end,
 				       __PAGE_KERNEL_RX);
 
-#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	kaiser_add_user_map_ptrs_early(__irqentry_text_start,
 				       __irqentry_text_end,
 				       __PAGE_KERNEL_RX);