drm/amdgpu: Prevent random memory access in FRU code

Prevent random memory access in the FRU EEPROM code by passing the size of
the destination buffer to the reading routine, and reading no more than the
size of the buffer.

Cc: Kent Russell <kent.russell@amd.com>
Cc: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>