Documentation: misc-devices: Rename freefall.c from hpfall.c in lis2lv02d

hpfall.c was renamed to freefall.c in 3.16, but this file still refer to
hpfall.c instead of freefall.c

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>