Fix kernel warning in ubd driver and release kernel

Whilst attempting to use UML as a backend to Debos a bug was triggered which resulted in UML failing to write to it's underlying image:

------------[ cut here ]------------
249 WARNING: CPU: 0 PID: 1616 at lib/refcount.c:28 refcount_sub_and_test.constprop.0+0x2a/0x30
250 refcount_t: underflow; use-after-free.
251 Modules linked in:
252 CPU: 0 PID: 1616 Comm: mkfs.ext2 Not tainted 5.6.0-rc1-11975-g77dafa3b732e-dirty #2
253 Stack:
254  e1148000 00000009 e11c6ba0 00000009
255  e11c6ba0 00000000 deaaec10 60047f36
256  e092d240 6011eb30 e092d240 e11c6c90
257 Call Trace:
258  [<6003ef2f>] ? os_is_signal_stack+0x17/0x23
259  [<6007745f>] ? printk+0x0/0x9b
260  [<603f821f>] ? blk_queue_max_discard_sectors+0x0/0xd
261  [<60029428>] ? show_stack+0x135/0x14e
262  [<60047f36>] ? __warn+0xf0/0x11a
263  [<6011eb30>] ? arch_local_irq_save+0x1d/0x22
264  [<600483bc>] ? warn_slowpath_fmt+0xd2/0xde
265  [<605a80ec>] ? xas_start+0x52/0x8a
266  [<600482ea>] ? warn_slowpath_fmt+0x0/0xde
267  [<60081c44>] ? raw_read_seqcount_begin.constprop.0+0x0/0x15
268  [<6003f494>] ? os_nsecs+0x18/0x2a
269  [<6007f138>] ? nsecs_to_jiffies64+0x0/0xe
270  [<603f457c>] ? arch_local_irq_save+0x1d/0x22
271  [<603fc479>] ? refcount_sub_and_test.constprop.0+0x2a/0x30

Add a series which addresses this issue and a few associated issues found whilst debugging. Release a new version of the kernel.