x86, dumpstack: Fix code bytes breakage due to missing KERN_CONT

When printing the code bytes in show_registers(), the markers around the
byte at the fault address could make the printk() format string look
like a valid log level and facility code.  This would prevent this byte
from being printed and result in a spurious newline:

[ 7555.765589] Code: 8b 32 e9 94 00 00 00 81 7d 00 ff 00 00 00 0f 87 96 00 00 00 48 8b 83 c0 00 00 00 44 89 e2 44 89 e6 48 89 df 48 8b 80 d8 02 00 00
[ 7555.765683]  8b 48 28 48 89 d0 81 e2 ff 0f 00 00 48 c1 e8 0c 48 c1 e0 04

Add KERN_CONT where needed, and elsewhere in show_registers() for
consistency.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Link: http://lkml.kernel.org/r/4EEFA7AE.9020407@ladisch.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>