f2fs: don't return vmalloc() memory from f2fs_kmalloc()

f2fs: don't return vmalloc() memory from f2fs_kmalloc()

kmalloc() returns kmalloc'ed memory, and kvmalloc() returns either
kmalloc'ed or vmalloc'ed memory.  But the f2fs wrappers, f2fs_kmalloc()
and f2fs_kvmalloc(), both return both kinds of memory.

It's redundant to have two functions that do the same thing, and also
breaking the standard naming convention is causing bugs since people
assume it's safe to kfree() memory allocated by f2fs_kmalloc().  See
e.g. the various allocations in fs/f2fs/compress.c.

Fix this by making f2fs_kmalloc() just use kmalloc().  And to avoid
re-introducing the allocation failures that the vmalloc fallback was
intended to fix, convert the largest allocations to use f2fs_kvmalloc().

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>