ibmraid: fix writeable attribute with no store method

https://bugzilla.kernel.org/show_bug.cgi?id=81311



 [ 0.603157] WARNING: at drivers/base/core.c:601
device_create_file+0x8d/0xa0()
 [ 0.603158] Attribute adapter_id: write permission without 'store'
 [ 0.603159] Modules linked in: i915(+) i2c_algo_bit drm_kms_helper drm
mpt2sas(+) pmcraid(+) raid_class scsi_transport_sas i2c_core video

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>