iwlwifi: Don't use buffer allocated on the stack for led names

Having the buffer on the stack and even re-using it for all led devices is bad.
Not being able to resolve the name member of the led device structure to a
meaningful value leads to confusion during ad-hoc debugging and potential
breakage in the future, if we ever decide to access the name member outside of
the registration function. Move the buffer to our private per led device
structures so that it is accessible after registration.

A quick grep didn't yield any occurence of using the led device name parameter
outside of the led device registration function, so currently we should already
be safe for normal operation.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Cc: Richard Purdie <rpurdie@rpsys.net>
Acked-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>