vsprintf: Update %pGp documentation about that it prints hex value

vsprintf: Update %pGp documentation about that it prints hex value

The commit 23efd0804c0a869dfb1e7 ("vsprintf: Make %pGp print
the hex value") changed the behavior of %pGp printk format.
Update the documentation accordingly.

Fixes: 23efd0804c0a869dfb1e7 ("vsprintf: Make %pGp print the hex value")
Reviewed-by: Yafang Shao <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/YXlKqCPY9suM4mfT@alley