arm64: fix show_data fallout from KERN_CONT changes

The log format printed by show_data is illegible due to printk change
"commit 4bcc595c ("printk: reinstate KERN_CONT for printing
continuation lines")".

The output is like:
[   32.669636] SP: 0xffffffc0b01f7c50:
[   32.669647] 7c50
[   32.669652]  b01f7eb0
[   32.669655]  ffffffc0
[   32.669659]  00000000
[   32.669662]  00000000
[   32.669665]  00000015
[   32.669669]  00000000
[   32.669672]  00000123
[   32.669675]  00000000
[   32.669674]
[   32.669680] 7c70
[   32.669684]  0000003f
[   32.669687]  00000000
[   32.669690]  08c82000
[   32.669694]  ffffff80
[   32.669697]  b01f4000
[   32.669700]  ffffffc0
[   32.669703]  b01f7cd0
[   32.669706]  ffffffc0

To fix this, use pr_cont() instead of the printk() to print
continuing lines.

Signed-off-by: Ji Zhang <ji.zhang@mediatek.com>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>