malloc null bugs

[Ted Unangst]

Found during analysis with Coverity's tools. FreeBSD 4.10
atapi-cd.c, everywhere.  I understand there was some question of not 
being to deal with failure gracefully in ata, but many of these are in 
functions like ioctl which can easily report errors.

igmp.c:find_rti
mii.c:mii_phy_probe.  device_add_child can also fail, and is not checked.
pst-raid.c:pst_add_raid
if_dc.c:dc_decode_leaf_mii
if_ti:ti_setmulti
if_sk.c:sk_vpd_read
uipc_syscalls.c:sf_buf_init

mpt.c:mpt_send_port_enable, mpt_get_request can fail

if_wi_pci.c:attach, bus_alloc_resource may fail