iwlwifi: avoid some operations if no uCode loaded

Printing the SRAM and similar testmode operations could
be triggered when no uCode is loaded; prevent those
invalid operations by tracking whether uCode is loaded.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>