staging: vchiq_arm: Clear VLA warning

staging: vchiq_arm: Clear VLA warning

The kernel would like to have all stack VLA usage removed[1]. The array
here is fixed (declared with a const variable) but it appears like a VLA
to the compiler. Also, currently we are putting 768 bytes on the
stack. This function is only called on the error path so performance is
not critical, let's just allocate the memory instead of using the
stack. This saves stack space and removes the VLA build warning.

kmalloc a buffer for dumping state instead of using the stack.

[1]: https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>