armv7m: Fix memory leak in register caching.

Change-Id: I184042d277a52f3940d6d6c13f3d94afc557933d
Signed-off-by: Marc Schink <openocd-dev@marcschink.de>
[andreas.fritiofson@gmail.com: don't check pointers before free()]
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/2881
Tested-by: jenkins

src/target/armv7m.h

@@ -186,6 +186,8 @@ struct armv7m_algorithm {
 };
 
 struct reg_cache *armv7m_build_reg_cache(struct target *target);
+void armv7m_free_reg_cache(struct target *target);
+
 enum armv7m_mode armv7m_number_to_mode(int number);
 int armv7m_mode_to_number(enum armv7m_mode mode);