[SCSI] ibmvscsi: Fix error path deadlock

Fixes a deadlock that can occur if we hit a command timeout
during the virtual adapter initialization. The event done
functions are written with the assumption that no locks are held,
however, when purging requests this is not true. Fix up the
purge function to drop the lock so that the done function
is not called with the lock held, which can cause a deadlock.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>