sim: constify sim_fpu_print_status

sim: constify sim_fpu_print_status

I've committed the following patch as obvious.  The local "prefix"
variable is only assigned const strings, and only passed to printf()
functions, so add "const" to avoid gcc warnings:
common/sim-fpu.c: In function 'sim_fpu_print_status':
common/sim-fpu.c:2508: warning: initialization discards qualifiers
	from pointer target type
common/sim-fpu.c:2566: warning: assignment discards qualifiers
	from pointer target type

Signed-off-by: Mike Frysinger <vapier@gentoo.org>