buildroot

jack2: add select on BR2_PACKAGE_ALSA_LIB_SEQ

The BR2_PACKAGE_ALSA_LIB_SEQ option is needed for jack2 to build
properly.

Fixes:

  http://autobuild.buildroot.org/results/fc4/fc42597a9a22af69a33c810561e2b3dd6c6bf8f4/

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