use mutex instead of semaphore in RocketPort driver

The RocketPort driver uses a semaphore as mutex.  Use the mutex API instead of
the (binary) semaphore.

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/rocket_int.h b/drivers/char/rocket_int.h
index 3a8bcc8..89b4d7b 100644
--- a/drivers/char/rocket_int.h
+++ b/drivers/char/rocket_int.h
@@ -15,6 +15,8 @@
 #define ROCKET_TYPE_MODEMIII	3
 #define ROCKET_TYPE_PC104       4
 
+#include <linux/mutex.h>
+
 #include <asm/io.h>
 #include <asm/byteorder.h>
 
@@ -1171,7 +1173,7 @@
 	struct wait_queue *close_wait;
 #endif
 	spinlock_t slock;
-	struct semaphore write_sem;
+	struct mutex write_mtx;
 };
 
 #define RPORT_MAGIC 0x525001