[media] saa7164: Remove pointless conditional and save a few bytes in saa7164_downloadfirmware()

Hi,

release_firmware() just does nothing if passed a NULL pointer. So there's
no reason to test before the call in
saa7164-fw.c::saa7164_downloadfirmware().

Removing the pointless conditional also saves a few bytes.
before:
   text    data     bss     dec     hex filename
   7943     112    2144   10199    27d7 drivers/media/video/saa7164/saa7164-fw.o
after:
   text    data     bss     dec     hex filename
   7931     112    2136   10179    27c3 drivers/media/video/saa7164/saa7164-fw.o

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Cc: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>