Stellaris: Print address of erased sector in hexadecimal

Some LPC chips respond to addressed in the region right above 4 GiB.
When printed in decimal, the address looks like a signed overflow.
Print the address in hexadecimal, which is a lot clearer, and exposes
any potential alignment issues.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>