V4L/DVB (8029): Improve error message at tda1004x_attach

When an error occurs at firmware loading, sometimes, tda1004x stops answering.
Instead of reporting such error, attach code were assuming that the device were
answering an invalid ID (0xff). This can be seen when enabling debug options:

tda1004x: tda1004x_read_byte: reg=0x0
tda1004x: tda1004x_read_byte: error reg=0x0, ret=-5

Now, instead of reporting an invalid ID, it will report the correct error:

tda10046: chip is not answering. Giving up.
saa7133[0]/dvb: failed to attach tda10046
saa7133[0]/dvb: frontend initialization failed

A possible improvement would be trying to reset the device.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>