nano2g: fix dangerous mutex in hold switch

This is a quick patch to solve FS#13104, we can not disable the
clickwheel LDO from within interrupt code, so for the moment we
leave it enabled all the time, it is unknown how power comsumption
is affected when the hold switch is locked.

Change-Id: I8f675702e2b5becbcd9197c8b044e6b8daeea79f
1 file changed