perf tools: Remove cast of non-variadic function to variadic

The 4fb71074

 (perf ui/hist: Consolidate hpp helpers) cset introduced
a cast of percent_color_snprintf to a function pointer type with
varargs.  Change percent_color_snprintf to be variadic and remove the
cast.

The symptom of this was all percentages being reported as 0.00% in perf
report --stdio output on the armhf arch.

Signed-off-by: Michael Hudson-Doyle <michael.hudson@linaro.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/87zjppvw7y.fsf@canonical.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>