cmd: sf: fix map_physmem check

Make sure 0x00 is a valid address to read to. If `addr` is 0x00 then
map_physmem() will return 0 which should be a valid address.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
1 file changed