gdi.exe16: Constify a variable

[Andrew Talbot]

Changelog:
    gdi.exe16: Constify a variable.

diff --git a/dlls/gdi.exe16/printdrv.c b/dlls/gdi.exe16/printdrv.c
index aee0e65..2060d9f 100644
--- a/dlls/gdi.exe16/printdrv.c
+++ b/dlls/gdi.exe16/printdrv.c
@@ -514,7 +514,7 @@ DWORD WINAPI GetSpoolJob16(int nOption, LONG param)
  *
  * Helper for DrvGetPrinterData
  */
-static DWORD DrvGetPrinterDataInternal(LPSTR RegStr_Printer,
+static DWORD DrvGetPrinterDataInternal(LPCSTR RegStr_Printer,
 LPBYTE lpPrinterData, int cbData, int what)
 {
     DWORD res = -1;