locking: Allow obtaining result of arch_mcs_spin_lock_contended

To support upcoming changes that require inspecting the return value
once the conditional waiting loop in arch_mcs_spin_lock_contended
terminates, modify the macro to preserve the result of
smp_cond_load_acquire. This enables checking the return value as needed,
which will help disambiguate the MCS node’s locked state in future
patches.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250316040541.108729-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: kkdwivedi

kernel/locking/mcs_spinlock.h

@@ -24,9 +24,7 @@
  * spinning, and smp_cond_load_acquire() provides that behavior.
  */
 #define arch_mcs_spin_lock_contended(l)					\
-do {									\
-	smp_cond_load_acquire(l, VAL);					\
-} while (0)
+	smp_cond_load_acquire(l, VAL)
 #endif
 
 #ifndef arch_mcs_spin_unlock_contended