mm/hmm: move pmd_to_hmm_pfn_flags() to the respective #ifdeffery

commit 188cb38 upstream.

When pmd_to_hmm_pfn_flags() is unused, it prevents kernel builds with
clang, `make W=1` and CONFIG_TRANSPARENT_HUGEPAGE=n:

  mm/hmm.c:186:29: warning: unused function 'pmd_to_hmm_pfn_flags' [-Wunused-function]

Fix this by moving the function to the respective existing ifdeffery
for its the only user.

See also:

  6863f56 ("kbuild: allow Clang to find unused static inline functions for W=1 build")

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 992de9a ("mm/hmm: allow to mirror vma of a file on a DAX backed filesystem")
Signed-off-by: Andy Shevchenko <[email protected]>
Reviewed-by: Leon Romanovsky <[email protected]>
Reviewed-by: Alistair Popple <[email protected]>
Cc: Andriy Shevchenko <[email protected]>
Cc: Bill Wendling <[email protected]>
Cc: Jerome Glisse <[email protected]>
Cc: Justin Stitt <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: andy-shev

mm/hmm.c

@@ -173,6 +173,7 @@ static inline unsigned long hmm_pfn_flags_order(unsigned long order)
 	return order << HMM_PFN_ORDER_SHIFT;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
 						 pmd_t pmd)
 {
@@ -183,7 +184,6 @@ static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
 	       hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
 }
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
 			      unsigned long end, unsigned long hmm_pfns[],
 			      pmd_t pmd)