sysvfs: fix NULL deref. when allocating new inode

A call to sysv_write_inode() in sysv_new_inode() to its new interface that
replaced wait flag with writeback structure.  This was broken by
a9185b41

 ("pass writeback_control to
->write_inode").

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@kernel.org>		[2.6.34.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>