FROMGIT: f2fs: increase the limit for reserve_root

This patch increases the threshold that limits the reserved root space from 0.2%
to 12.5% by using simple shift operation.

Typically Android sets 128MB, but if the storage capacity is 32GB, 0.2% which is
around 64MB becomes too small. Let's relax it.

Bug: 243493735
Cc: stable@vger.kernel.org
Reported-by: Aran Dalton <arda@allwinnertech.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Change-Id: Ia76ae8f9dd1c7a5f123a561f081bf5a4a29ac186
(cherry picked from commit cf42f1d7ab33ea2637f3c6b786a76302f719726b
     https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git dev)