musl-obstack: Update to 1.2.3

Switch to void-linux github handle, void-linux is the upstream anyway this brings

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>