This fixes:
  MODPOST 393 modules
ERROR: "min_low_pfn" [arch/mips/kvm/kvm.ko] undefined!
make[3]: *** [__modpost] Error 1
It would have been possible to just export min_low_pfn but in the end
pfn_valid should return 1 for any pfn argument for which a struct page
exists so using min_low_pfn was wrong anyway.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
 
 #ifdef CONFIG_FLATMEM
 
-#define pfn_valid(pfn)                                                 \
-({                                                                     \
-       unsigned long __pfn = (pfn);                                    \
-       /* avoid <linux/bootmem.h> include hell */                      \
-       extern unsigned long min_low_pfn;                               \
-                                                                       \
-       __pfn >= min_low_pfn && __pfn < max_mapnr;                      \
-})
+static inline int pfn_valid(unsigned long pfn)
+{
+       /* avoid <linux/mm.h> include hell */
+       extern unsigned long max_mapnr;
+
+       return pfn >= ARCH_PFN_OFFSET && pfn < max_mapnr;
+}
 
 #elif defined(CONFIG_SPARSEMEM)