x86/mm: use block_lock_speculation() in _mm_write_lock()

I can only guess that using block_speculation() there was a leftover
from, earlier on, SPECULATIVE_HARDEN_LOCK depending on
SPECULATIVE_HARDEN_BRANCH.

Fixes: 197ecd838a ("locking: attempt to ensure lock wrappers are always inline")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/mm/mm-locks.h

@@ -138,7 +138,7 @@ static always_inline void _mm_write_lock(const struct domain *d, mm_rwlock_t *l,
         _set_lock_level(_lock_level(d, level));
     }
     else
-        block_speculation();
+        block_lock_speculation();
     l->recurse_count++;
 }