mm/hmm: don't provide a stub for hmm_range_fault()

All callers of hmm_range_fault depend on CONFIG_HMM_MIRROR, so don't
bother with a stub.

Link: https://lore.kernel.org/r/20200316135310.899364-2-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/linux/hmm.h

@@ -225,17 +225,10 @@ static inline uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
 /* Don't fault in missing PTEs, just snapshot the current state. */
 #define HMM_FAULT_SNAPSHOT		(1 << 1)
 
-#ifdef CONFIG_HMM_MIRROR
 /*
  * Please see Documentation/vm/hmm.rst for how to use the range API.
  */
 long hmm_range_fault(struct hmm_range *range, unsigned int flags);
-#else
-static inline long hmm_range_fault(struct hmm_range *range, unsigned int flags)
-{
-	return -EOPNOTSUPP;
-}
-#endif
 
 /*
  * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range