s390/mm: Get rid of RELOC_HIDE()

Since __va(0) does not translate to NULL anymore remove RELOC_HIDE()
which was only added to get rid of a compile warning with clang W=1:

    arch/s390/mm/vmem.c:666:36: warning: performing pointer arithmetic on
     a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
      666 |                 __set_memory_4k(__va(0), __va(0) + ident_map_size);
          |                                          ~~~~~~~ ^
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/mm/vmem.c

@@ -670,14 +670,8 @@ void __init vmem_map_init(void)
 	 */
 	if (!static_key_enabled(&cpu_has_bear))
 		set_memory_x(0, 1);
-	if (debug_pagealloc_enabled()) {
-		/*
-		 * Use RELOC_HIDE() as long as __va(0) translates to NULL,
-		 * since performing pointer arithmetic on a NULL pointer
-		 * has undefined behavior and generates compiler warnings.
-		 */
-		__set_memory_4k(__va(0), RELOC_HIDE(__va(0), ident_map_size));
-	}
+	if (debug_pagealloc_enabled())
+		__set_memory_4k(__va(0), __va(0) + ident_map_size);
 	if (MACHINE_HAS_NX)
 		system_ctl_set_bit(0, CR0_INSTRUCTION_EXEC_PROTECTION_BIT);
 	pr_info("Write protected kernel read-only data: %luk\n",