bluez5_utils: improved version of the mcaptest patch

As suggested by bluez5_utils upstream developers, use an improved
version of the mcaptest patch that only conditionally links on librt
instead of unconditionally linking against it (glibc after 2.17 have
clock_getres() in libc and not in librt).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>