SPARC: Make sure that jump is to a label in errata workaround

SPARC: Make sure that jump is to a label in errata workaround

In some cases the jump could be to a return instruction and in those cases the
next_active_insn() function tries to follow an invalid pointer which leads to a
crash. This error did not manifest when using a 32-bit version of GCC which is
why I did not detect it before.

gcc/
	* config/sparc/sparc.c (sparc_do_work_around_errata): Make sure
	the jump is to a label.

From-SVN: r255807