rtlwifi: fix null dereference on efuse_word on kmalloc fail returns NULL

kmalloc on efuse_word can return null, leading to free'ing of
elements in efuse_word on the error exit path even though it has not
been allocated.  Instead, don't free the elements of efuse_word if
kmalloc failed.

Also, kmalloc of any of the arrays in efuse_word[] can also fail,
leading to undefined contents in the remaining elements leading to
problems when free'ing these elements later on.  So kzalloc efuse_word
to ensure the kfree on the remaining elements won't cause breakage.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>