zdump: write_dump: use FILE *

Use the more common `FILE *` for writing to the output.

Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdump/output.h

@@ -8,6 +8,8 @@
 #ifndef OUTPUT_H
 #define OUTPUT_H
 
-int write_dump(int fd);
+#include <stdio.h>
+
+int write_dump(FILE *stream);
 
 #endif /* OUTPUT_H */