cleanup process_usb_op() / process_scsi_op() declarations

Commit 1e749c85 removed the definition of process_usb_op(); let's remove
the declaration too.

The same commit added process_scsi_op(). The function has no declaration
that is also not a definition, and its only call site is in the same file
as the definition. Give the function internal linkage.

Build tested.

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
diff --git a/src/block.c b/src/block.c
index eeebd83..ccf4ee6 100644
--- a/src/block.c
+++ b/src/block.c
@@ -276,7 +276,7 @@
  * 16bit calling interface
  ****************************************************************/
 
-int
+static int
 process_scsi_op(struct disk_op_s *op)
 {
     if (!CONFIG_USB_MSC)
diff --git a/src/usb-msc.h b/src/usb-msc.h
index a8686a3..12d749c 100644
--- a/src/usb-msc.h
+++ b/src/usb-msc.h
@@ -8,7 +8,6 @@
 struct usb_pipe;
 int usb_msc_init(struct usb_pipe *pipe
                  , struct usb_interface_descriptor *iface, int imax);
-int process_usb_op(struct disk_op_s *op);
 
 
 /****************************************************************