media: atomisp: don't cause a warn if probe failed

When probe fails, it is possible that hmm_init() to not be
called. On such case, hmm_cleanup() will cause a WARN_ON().

Avoid it by adding an explicit check at hmm_cleanup() to
ensure that the hmm code was properly initialized.

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