trivial: doc: hpfall: accept disk device to unload as argument
trivial: doc: hpfall: accept disk device to unload as argument

Allows users who use an IDE driver for their disk to use hpfall without
having to modify the source. By default /dev/sda is used.
Suggested by Christian Thaeter in http://lkml.org/lkml/2009/3/25/505.

While we're add it, improve error message if opening /dev/freefall fails.

Signed-off-by: Frans Pop <1dac9bba9cb569a6a8c1c01dfb685827c24c1aa3@planet.nl>
Cc: Christian Thaeter <589e942e00a7dd64a273deb5041c7ce469f2bad7@pipapo.org>
Acked-by: Pavel Machek <2375fa63e2908bb2df59f606483a3aa92321db7a@ucw.cz>
Signed-off-by: Jiri Kosina <ed58f755cc8caaf10c3e8c731a8b86fb8f13d6cb@suse.cz>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas