iwlwifi: mvm: fix missing cleanup in .start() error path

iwlwifi: mvm: fix missing cleanup in .start() error path

Cleanup of iwl_mvm_leds was missing in case of error,
resulting in the following warning:

WARNING: at lib/kobject.c:196 kobject_add_internal+0x1f4/0x210()
kobject_add_internal failed for phy0-led with -EEXIST, don't try to register things with the same name in the same directory.

which prevents further reloads of the driver.

Cc: stable@vger.kernel.org [3.10+]
Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>