ehea: fix might sleep problem

A mutex has to be replaced by spinlocks as it can be called from
a context which does not allow sleeping.
The kzalloc flag GFP_KERNEL has to be replaced by GFP_ATOMIC
for the same reason.

Signed-off-by: Jan-Bernd Themann <themann@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>