media: allegro: add missed checks in allegro_open()

allegro_open() misses checks for v4l2_m2m_ctx_init() and results of
v4l2_ctrl_new* calls.
Add checks and error handlers to fix the problems.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>