media: m920x: don't use stack on USB reads

Using stack-allocated pointers for USB message data don't work.
This driver is almost OK with that, except for the I2C read
logic.

Fix it by using a temporary read buffer, just like on all other
calls to m920x_read().

Link: https://lore.kernel.org/all/ccc99e48-de4f-045e-0fe4-61e3118e3f74@mida.se/


Reported-by:  <rkardell@mida.se>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>