media: saa7146: hexium_gemini: Fix a NULL pointer dereference in hexium_attach()

media: saa7146: hexium_gemini: Fix a NULL pointer dereference in hexium_attach()

In hexium_attach(dev, info), saa7146_vv_init() is called to allocate
a new memory for dev->vv_data. saa7146_vv_release() will be called on
failure of saa7146_register_device(). There is a dereference of
dev->vv_data in saa7146_vv_release(), which could lead to a NULL
pointer dereference on failure of saa7146_vv_init().

Fix this bug by adding a check of saa7146_vv_init().

This bug was found by a static analyzer. The analysis employs
differential checking to identify inconsistent security operations
(e.g., checks or kfrees) between two code paths and confirms that the
inconsistent operations are not recovered in the current function or
the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

Builds with CONFIG_VIDEO_HEXIUM_GEMINI=m show no new warnings,
and our static analyzer no longer warns about this code.

Link: https://lore.kernel.org/linux-media/20211203154030.111210-1-zhou1615@umn.edu
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>