buildroot

package makefiles: clean up backslash spacing.

The check-package script when ran gave warnings on only using
one space before backslashes on all of these makefiles.
This patch cleans up all warnings related to the one space before
backslashes rule in the make files in the package directory.

Signed-off-by: Adam Duskett <aduskett@codeblue.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>