net-print/hpuld: add -r4 with libxml2-compat:2, drop -r3

- libsane-smfp.so.1.0.1 needs libxml2.so.2 but libxml2-2.14+ dropped it.
- dev-libs/libxml2-compat installs the .so.2 SONAME for prebuilt blobs.

Closes: https://bugs.gentoo.org/975969
Signed-off-by: Huang Rui <vowstar@gmail.com>

net-print/hpuld/hpuld-1.00.39.15.00.23-r4.ebuild

@@ -25,7 +25,7 @@ RDEPEND="
 	dev-libs/libusb
 	net-print/cups
 	scanner? (
-		dev-libs/libxml2:2
+		dev-libs/libxml2-compat:2
 		media-gfx/sane-backends
 	)
 "