musb_core: don't touch 'musb->clock' in musb_free()

Remove duplicate/unbalanced calls to clk_disable()/clk_put() in musb_free():

- clk_disable() is called by musb_platform_exit() just prior to this call;
- clk_put() is called by the callers of musb_free() prior to calling it...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>