winspool.drv: Cast-qual warning fix + make function static

[Andrew Talbot]

Changelog:
    winspool.drv: Cast-qual warning fix + make function static.

diff -urN a/dlls/winspool.drv/info.c b/dlls/winspool.drv/info.c
--- a/dlls/winspool.drv/info.c	2006-11-17 20:11:48.000000000 +0000
+++ b/dlls/winspool.drv/info.c	2006-11-23 21:09:42.000000000 +0000
@@ -383,7 +383,7 @@
     }
 }
 
-BOOL add_printer_driver(const char *name)
+static BOOL add_printer_driver(char *name)
 {
     DRIVER_INFO_3A di3a;