media: lgdt3306a: Add a check against null-pointer-def

In the Linux kernel, the following vulnerability has been resolved:

media: lgdt3306a: Add a check against null-pointer-def

The driver should check whether the client provides the platform_data.

The following log reveals it:

[ 29.610324] BUG: KASAN: null-ptr-deref in kmemdup+0x30/0x40

[ 29.610730] Read of size 40 at addr 0000000000000000 by task bash/414

[ 29.612820] Call Trace:

[ 29.613030] <TASK>

[ 29.613201] dump_stack_lvl+0x56/0x6f

[ 29.613496] ? kmemdup+0x30/0x40

[ 29.613754] print_report.cold+0x494/0x6b7

[ 29.614082] ? kmemdup+0x30/0x40

[ 29.614340] kasan_report+0x8a/0x190

[ 29.614628] ? kmemdup+0x30/0x40

[ 29.614888] kasan_check_range+0x14d/0x1d0

[ 29.615213] memcpy+0x20/0x60

[ 29.615454] kmemdup+0x30/0x40

[ 29.615700] lgdt3306a_probe+0x52/0x310

[ 29.616339] i2c_device_probe+0x951/0xa90