mptfusion: hide unused seq_mpt_print_ioc_summary function

The seq_mpt_print_ioc_summary function is used for the
/proc/mpt/iocN/summary implementation and never gets called when
CONFIG_PROC_FS is disabled:

drivers/message/fusion/mptbase.c:6851:13: warning: 'seq_mpt_print_ioc_summary' defined but not used [-Wunused-function]
 static void seq_mpt_print_ioc_summary(MPT_ADAPTER *ioc, struct seq_file *m, int showlan)

This adds an #ifdef to hide the function definition in that case and
avoid the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>