jffs2: fix memory leak in jffs2_do_mount_fs

In the Linux kernel, the following vulnerability has been resolved:

jffs2: fix memory leak in jffs2_do_mount_fs

If jffs2_build_filesystem() in jffs2_do_mount_fs() returns an error,

we can observe the following kmemleak report:

--------------------------------------------

unreferenced object 0xffff88811b25a640 (size 64):

comm "mount", pid 691, jiffies 4294957728 (age 71.952s)

hex dump (first 32 bytes):

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

backtrace:

[<ffffffffa493be24>] kmem_cache_alloc_trace+0x584/0x880

[<ffffffffa5423a06>] jffs2_sum_init+0x86/0x130

[<ffffffffa5400e58>] jffs2_do_mount_fs+0x798/0xac0

[<ffffffffa540acf3>] jffs2_do_fill_super+0x383/0xc30

[<ffffffffa540c00a>] jffs2_fill_super+0x2ea/0x4c0

[...]

unreferenced object 0xffff88812c760000 (size 65536):

comm "mount", pid 691, jiffies 4294957728 (age 71.952s)

hex dump (first 32 bytes):

bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................

bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb ................

backtrace:

[<ffffffffa493a449>] __kmalloc+0x6b9/0x910

[<ffffffffa5423a57>] jffs2_sum_init+0xd7/0x130

[<ffffffffa5400e58>] jffs2_do_mount_fs+0x798/0xac0

[<ffffffffa540acf3>] jffs2_do_fill_super+0x383/0xc30

[<ffffffffa540c00a>] jffs2_fill_super+0x2ea/0x4c0

[...]

--------------------------------------------

This is because the resources allocated in jffs2_sum_init() are not

released. Call jffs2_sum_exit() to release these resources to solve

the problem.