hfsplus: Fix double iput of the same inode in hfsplus_fill_super()

There is a misprint in resource deallocation code on error path in
hfsplus_fill_super(): the sbi->alloc_file inode is iput twice,
while the root inode in not iput at all.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Christoph Hellwig <hch@lst.de>