[S390] partitions: fix build error in ibm partition detection code

9c867fbe "partitions: fix sometimes unreadable partition strings" coverted
one line within the ibm partition code incorrectly. Fix this to get rid of
a build error.

fs/partitions/ibm.c: In function 'ibm_partition':
[...]
fs/partitions/ibm.c:185: error: too many arguments to function 'strlcat'

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>