package/lcms2: fix static building with tiff

Strangely enough, we have only one build failure on the autobuilder even
if lcms2 never used pkg-config to retrieve static dependencies of tiff
(which also depends on xz since 2016)

Fixes:
 - http://autobuild.buildroot.org/results/07c5ca780bcdbfcd7cad6502345f1553ce17bdc3



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>