lib/bitmap: extend comment for bitmap_(from,to)_arr32()

On LE systems bitmaps are naturally ordered, therefore we can potentially
use bitmap_copy routines when converting from 32-bit arrays, even if host
system is 64-bit. But it may lead to out-of-bond access due to unsafe
typecast, and the to the bitmap_(from,to)_arr32 comment doesn't explain
that clearly

include/linux/bitmap.h

@@ -271,10 +271,14 @@ static inline void bitmap_copy_clear_tail(unsigned long *dst,
 }
 
 /*
- * On 32-bit systems bitmaps are represented as u32 arrays internally, and
- * therefore conversion is not needed when copying data from/to arrays of u32.
+ * On 32-bit systems bitmaps are represented as u32 arrays internally. On LE64
+ * machines the order of hi and lo parts of nubmers match the bitmap structure.
+ * In both cases conversion is not needed when copying data from/to arrays of
+ * u32. But in LE64 case, typecast in bitmap_copy_clear_tail() may lead
+ * to out-of-bound access. To avoid that, both LE and BE variants of 64-bit
+ * architectures are not using bitmap_copy_clear_tail().
  */
-#if BITS_PER_LONG == 64
+#if (BITS_PER_LONG == 64)
 void bitmap_from_arr32(unsigned long *bitmap, const u32 *buf,
 							unsigned int nbits);
 void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap,

lib/bitmap.c

@@ -1487,7 +1487,7 @@ unsigned long *devm_bitmap_zalloc(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_bitmap_zalloc);
 
-#if BITS_PER_LONG == 64
+#if (BITS_PER_LONG == 64)
 /**
  * bitmap_from_arr32 - copy the contents of u32 array of bits to bitmap
  *	@bitmap: array of unsigned longs, the destination bitmap