staging: r8188eu: check firmware header existence before access

We should access the fields of fwhdr only if the check for firmware
header existence is true. Move the affected code into the if block
that checks firmware header existence.

Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220417175441.13830-9-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>