accel: ethosu: Ensure SRAM region size matches job

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

accel: ethosu: Ensure SRAM region size matches job

It is possible for userspace to set the job SRAM size to 0, but then still
have SRAM accesses in the command stream. When the job SRAM size is 0,
setting the region base register is skipped and a stale base address from
a prior job is used.

Check the region size against the job's SRAM size instead of just the size
of the SRAM. The job's SRAM size was already checked against the total SRAM
size.