eudev: don't test if the binary exists in the init script

eudev: don't test if the binary exists in the init script

The test doesn't make sense. It just exits with error code 5 if the
binary doesn't exist, which is silly. Buildroot installs both udevd and
its init script as part of the same package. But if it ever happens for
some reason, the error message "/sbin/udevd: No such file or directory"
in the start case should be pretty clear.

Replace the UDEV_BIN variable, which was used only once, by the full
path of the binary file.

Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>