drm/amdkfd: print doorbell offset as a hex value

The doorbell offset is formatted with a 0x prefix to suggest it is
a hexadecimal value, when in fact %d is being used and this is confusing.
Use %X instead to match the proceeding 0x prefix.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>