iwl: cleanup: remove unneeded error handling

This is just a cleanup and doesn't change how the code works.

debugfs_create_dir() and debugfs_create_file() return an error pointer
(-ENODEV) if CONFIG_DEBUG_FS is not enabled, otherwise if an error occurs
they return NULL.  This is how they are implemented and what it says in
the DebugFS documentation.  DebugFS can not be compiled as a module.

As a result, we only need to check for error pointers and particularly
-ENODEV one time to know that DebugFS is enabled.  This patch keeps the
first check for error pointers and removes the rest.

The other reason for this patch, is that it silences some Smatch warnings.
Smatch sees the condition "(result != -ENODEV)" and assumes that it's
possible for "result" to equal -ENODEV.  If it were possible it would lead
to an error pointer dereference.  But since it's not, we can just remove
the check.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>