scripts/get_abi.pl: avoid creating duplicate names

scripts/get_abi.pl: avoid creating duplicate names

The file the Documentation/ABI/testing/sysfs-class-power has
voltage_min, voltage_max and voltage_now symbols duplicated.

They are defined first for "General Properties" and then for
"USB Properties".

This cause those warnings:

	get_abi.pl rest --dir $srctree/Documentation/ABI/testing:26933: WARNING: Duplicate explicit target name: "abi_sys_class_power_supply_supply_name_voltage_max".
	get_abi.pl rest --dir $srctree/Documentation/ABI/testing:26968: WARNING: Duplicate explicit target name: "abi_sys_class_power_supply_supply_name_voltage_min".
	get_abi.pl rest --dir $srctree/Documentation/ABI/testing:27008: WARNING: Duplicate explicit target name: "abi_sys_class_power_supply_supply_name_voltage_now".

And, as the references are not valid, it will also generate
warnings about links to undefined references.

Fix it by storing labels into a hash table and, when a duplicated
one is found, appending random characters at the end.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>