USB: musb: tusb6010: fix compile error with n8x0_defconfig

Drop the unnecessary empty stubs in tusb6010.c and avoid
a compile error when building kernel for n8x0.

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>