curses: Make float2str static

Fix sparse message:
out_curses.c:140:6: warning: symbol 'float2str' was not declared. Should it be static?

Signed-off-by: Thomas Graf <tgraf@suug.ch>

src/out_curses.c

@@ -137,7 +137,7 @@ static void apply_layout(int layout)
 		attrset(cfg_layout[layout].l_attr);
 }
 
-char *float2str(double value, int width, int prec, char *buf, size_t len)
+static char *float2str(double value, int width, int prec, char *buf, size_t len)
 {
 	snprintf(buf, len, "%'*.*f", width, value == 0.0f ? 0 : prec, value);