UBIFS: fix a typo in comment of ubifs_budget_req

s/now/how

CRs-Fixed: 975289
Change-Id: I485d59980381e9e33515779fcb68d860c8b95800
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Git-commit: 7d25b361a2d3e8a9dcaf463d92285d58dedc74ab
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>