krnl386.exe16: Constify a variable

[Andrew Talbot]

Changelog:
    krnl386.exe16: Constify a variable.

diff --git a/dlls/krnl386.exe16/dosexe.c b/dlls/krnl386.exe16/dosexe.c
index 9797c86..ff96554 100644
--- a/dlls/krnl386.exe16/dosexe.c
+++ b/dlls/krnl386.exe16/dosexe.c
@@ -238,7 +238,7 @@ static BOOL MZ_DoLoadImage( HANDLE hFile, LPCSTR filename, OverlayBlock *oblk, W
  if (   !ReadFile(hFile,&mz_header,sizeof(mz_header),&len,NULL)
      || len != sizeof(mz_header)
      || mz_header.e_magic != IMAGE_DOS_SIGNATURE) {
-  char *p = strrchr( filename, '.' );
+  const char *p = strrchr( filename, '.' );
   if (!p || strcasecmp( p, ".com" ))  /* check for .COM extension */
   {
       SetLastError(ERROR_BAD_FORMAT);