s390/dis: use correct escape sequence for '%' character

s390/dis: use correct escape sequence for '%' character

The double escape character sequence introduced with commit
f3395b260c71 ("s390/dis: Fix handling of format specifiers") is not
necessary anymore since commit d9433fb2041e ("s390/dis: Fix printing
of the register numbers").

Instead this now generates an extra '%' character:

lg      %%r1,160(%%r11)

So fix this and basically revert f3395b260c71.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>