BKL-removal: convert ext2 over to use unlocked_ioctl

I checked ext2_ioctl and could not find anything in there that would need the
BKL.  So convert it over to use unlocked_ioctl

Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>