iwlwifi: fix potential buffer overrun in fw name

Fix a potential buffer overrun when creating the fw name
in drv->firmware_name by setting a maximal length to the
char array copied to it.
The maximal length is also updated to 32 rather than 25 to
keep both 32bit and 64bit alignment without requiring
padding to the struct it is in.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>