BeagleBone slots file location changed in Kernel 4.1+

[douglas-gibbons]

Kernel 4.1+ changed the name of the slots directory from:
/sys/devices/bone_capemgr.*/slots
to
/sys/devices/platform/bone_capemgr/slots

The fix for me was a pattern change in lines 102 and 131 of embd/host/bbb/bbb.go

Let me know if you need a pr.