package/opencv: cleanup spaces at ends of line

Nothing more than removing white spaces before '\' characters.
Of course, 'git diff -w' shows no change at all.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>