media: venus: hfi: return an error if session_init is already called

This makes hfi_session_init to return an error when it is
already called without a call to hfi_session_deinit.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>