util: file: Fix usage of STRPREFIX in virFileIsCDROM

STRPREFIX takes only two arguments, but the code it was adapted from
used function with 3 arguments.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>

src/util/virfile.c

@@ -1982,8 +1982,8 @@ virFileIsCDROM(const char *path)
 int
 virFileIsCDROM(const char *path)
 {
-    if (STRPREFIX(path, "/dev/cd", NULL) ||
-        STRPREFIX(path, "/dev/acd", NULL))
+    if (STRPREFIX(path, "/dev/cd") ||
+        STRPREFIX(path, "/dev/acd"))
         return 1;
 
     return 0;