media: si2157: unknown chip version Si2147-A30 ROM 0x50

Fix firmware file names assignment in si2157 tuner, allow for running
devices without firmware files needed.

modprobe gives error: unknown chip version Si2147-A30 ROM 0x50
Device initialization is interrupted.

Caused by:
1. table si2157_tuners has swapped fields rom_id and required vs struct
   si2157_tuner_info.
2. both firmware file names can be null for devices with
   required == false - device uses build-in firmware in this case

Tested on this device:
	m07ca:1871 AVerMedia Technologies, Inc. TD310 DVB-T/T2/C dongle

[mchehab: fix mangled patch]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215726
Link: https://lore.kernel.org/lkml/5f660108-8812-383c-83e4-29ee0558d623@leemhuis.info/
Link: https://lore.kernel.org/linux-media/c4bcaff8-fbad-969e-ad47-e2c487ac02a1@gmail.com
Fixes: 1c35ba3b

 ("media: si2157: use a different namespace for firmware")
Cc: stable@vger.kernel.org # 5.17.x
Signed-off-by: Piotr Chmura <chmooreck@gmail.com>
Tested-by: Robert Schlabbach <robert_s@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>