x86/head64: Add missing __head annotation to sme_postprocess_startup()

This function was previously part of __startup_64() which is marked
__head, and is currently only called from there. Mark it __head too.
Signed-off-by: Marco Bonelli <marco@mebeim.net>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220211162350.11780-1-marco@mebeim.net

arch/x86/kernel/head64.c

@@ -126,7 +126,7 @@ static bool __head check_la57_support(unsigned long physaddr)
 }
 #endif
 
-static unsigned long sme_postprocess_startup(struct boot_params *bp, pmdval_t *pmd)
+static unsigned long __head sme_postprocess_startup(struct boot_params *bp, pmdval_t *pmd)
 {
 	unsigned long vaddr, vaddr_end;
 	int i;