shader_runner: sscanf returns incorrect value on 32-bit build

A number of tests were reporting failure on 32-bit build, due to sscanf incorrectly parsing hexadecimal values of -0.0 and NaN.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107677

Signed-off-by: Yevhenii Kolesnikov yevhenii.kolesnikov@globallogic.com