s390/atomic,cmpxchg: always inline __xchg/__cmpxchg

Make sure to always inline __xchg() and __cmpxchg() otherwise the
compiler might decide to generate out-of-line versions which will
fail at link time:

   s390-linux-ld: lib/atomic64_test.o: in function `__xchg':
>> atomic64_test.c:(.text.unlikely+0xa4): undefined reference to `__xchg_called_with_bad_pointer'

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/linux-mm/202104170449.SIIFKVjT-lkp@intel.com/
Fixes: d2b1f6d ("s390/cmpxchg: get rid of gcc atomic builtins")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/cmpxchg.h

@@ -14,7 +14,8 @@
 
 void __xchg_called_with_bad_pointer(void);
 
-static inline unsigned long __xchg(unsigned long x, unsigned long address, int size)
+static __always_inline unsigned long __xchg(unsigned long x,
+					    unsigned long address, int size)
 {
 	unsigned long old;
 	int shift;
@@ -83,8 +84,9 @@ static inline unsigned long __xchg(unsigned long x, unsigned long address, int s
 
 void __cmpxchg_called_with_bad_pointer(void);
 
-static inline unsigned long __cmpxchg(unsigned long address, unsigned long old,
-				      unsigned long new, int size)
+static __always_inline unsigned long __cmpxchg(unsigned long address,
+					       unsigned long old,
+					       unsigned long new, int size)
 {
 	unsigned long prev, tmp;
 	int shift;