usb/storage/ene_ub6250: Remove redundant NULL check before release_firmware() and pointless assignment

release_firmware() tests for a NULL pointer, so it's redundant to do
that checking before calling it.

Additionally, in ene_load_bincode(), 'sd_fw' is a local variable so
setting it to NULL just before it goes out of scope is completely
pointless, so remove that assignment.
Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>