Behaviour of bitmap_fill() differs from bitmap_zero() in a way how bits
behind bitmap are handed.  bitmap_zero() clears entire bitmap by unsigned
long boundary, while bitmap_fill() mimics bitmap_set().

Here we change bitmap_fill() behaviour to be consistent with bitmap_zero()
and add a note to documentation.

The change might reveal some bugs in the code where unused bits are
handled differently and in such cases bitmap_set() has to be used.

Link: http://lkml.kernel.org/r/20180109172430.87452-4-andriy.shevchenko@linux.intel.comSigned-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Yury Norov <ynorov@caviumnetworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>