util: Use reg_belongs_to_class instead of BITSET_TEST
util: Use reg_belongs_to_class instead of BITSET_TEST

This shouldn't be a functional change since reg_belongs_to_class is just a
wrapper around BITSET_TEST.  It just makes the code a little easier to
read.

Signed-off-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler