docs: printk-formats: Fix hex printing of signed values

The commit cbacb5ab ("docs: printk-formats: Stop encouraging use of
unnecessary %h[xudi] and %hh[xudi]") obviously missed the point of sign
promotion for the signed values lesser than int. In such case %x prints
not the same as %h[h]x. Restore back those specifiers for the signed hex
cases.

Fixes: cbacb5ab ("docs: printk-formats: Stop encouraging use of unnecessary %h[xudi] and %hh[xudi]")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230703145839.14248-1-andriy.shevchenko@linux.intel.com