jfs: fix metapage reference count leak in dbAllocCtl

In dbAllocCtl(), read_metapage() increases the reference count of the
metapage. However, when dp->tree.budmin < 0, the function returns -EIO
without calling release_metapage() to decrease the reference count,
leading to a memory leak.

Add release_metapage(mp) before the error return to properly manage
the metapage reference count and prevent the leak.

Fixes: a5f5e469 ("jfs: fix shift-out-of-bounds in dbSplit")

Signed-off-by: Zheng Yu <zheng.yu@northwestern.edu>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>