media: lgdt3306a: fix a missing check of return value

If lgdt3306a_read_reg() fails, the read data in "val" is incorrect, thus
shouldn't be further used. The fix inserts a check for the return value
of lgdt3306a_read_reg(). If it fails, goto fail.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>