Uninitialised variable in common/spl/spl_imx_container.c

[Andrew Goodbody]

The commit 73c40fcb7367f5a spl: Refactor spl_load_info->read to use 
units of bytes by Sean Anderson <seanga2 at gmail.com> on 2023-11-08 
16:48:40 introduced the variable 'overhead' in the function 
read_auth_image and it is referenced only once where its value is 
attempted to be used in that function but it is never assigned a value.

This produces a Smatch error
common/spl/spl_imx_container.c:57 read_auth_image() error: uninitialized 
symbol 'overhead'.

The resolution to this error is not immediately obvious to me so if 
anyone would like to take a look please?

Thanks,
Andrew