rtlwifi: remove redundant assignment to variable err

Variable err is assigned -ENODEV followed by an error return path
via label error_out that does not access the variable and returns
with the -ENODEV error return code. The assignment to err is
redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210327230014.25554-1-colin.king@canonical.com