fs/jfs: Add check for negative db_l2nbperpage

mainline inclusion
from mainline-v6.7-rc1
commit 525b861a008143048535011f3816d407940f4bfa
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9RFEZ
CVE: CVE-2023-52810

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=525b861a008143048535011f3816d407940f4bfa



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l2nbperpage is log2(number of blks per page), and the minimum legal
value should be 0, not negative.

In the case of l2nbperpage being negative, an error will occur
when subsequently used as shift exponent.

Syzbot reported this bug:

UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:799:12
shift exponent -16777216 is negative

Reported-by:  <syzbot+debee9ab7ae2b34b0307@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=debee9ab7ae2b34b0307


Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Li Nan <linan122@huawei.com>