local: Fix prefix detection
local: Fix prefix detection

For prefix detection make sure that the prefix is always followed by a '_'.
Otherwise we might end up detecting the name of the attribute as the
prefix. E.g. if the channel has the following attributes:

	in_voltage0_foobar
	in_voltage0_foobar_available

foobar would previously incorrectly be detected has the channel prefix.

Signed-off-by: Lars-Peter Clausen <3318dc5ce3e4fb7c28a0b841b6801c884e1d0896@metafoo.de>

gburca/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,gburca/libiio,analogdevicesinc/libiio,gburca/libiio,analogdevicesinc/libiio