linux/bitmap.h: relax comment on compile-time constant nbits

It's not clear what's so horrible about emitting a function call to handle
a run-time sized bitmap.  Moreover, gcc also emits a function call for a
compile-time-constant-but-huge nbits, so the comment isn't even accurate.

Link: http://lkml.kernel.org/r/20180818131623.8755-6-linux@rasmusvillemoes.dkSigned-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Yury Norov <ynorov@caviumnetworks.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/bitmap.h

@@ -28,8 +28,8 @@
  * The available bitmap operations and their rough meaning in the
  * case that the bitmap is a single unsigned long are thus:
  *
- * Note that nbits should be always a compile time evaluable constant.
- * Otherwise many inlines will generate horrible code.
+ * The generated code is more efficient when nbits is known at
+ * compile-time and at most BITS_PER_LONG.
  *
  * ::
  *