ipr: Fix regression when loading firmware

Commit d63c7dd5 ("ipr: Fix out-of-bounds null overwrite") removed
the end of line handling when storing the update_fw sysfs attribute.
This changed the userpace API because it started refusing writes
terminated by a line feed, which broke the update tools we already have.

This patch re-adds that handling, so both a write terminated by a line
feed or not can make it through with the update.

Fixes: d63c7dd5 ("ipr: Fix out-of-bounds null overwrite")
Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
Cc: Insu Yun <wuninsu@gmail.com>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>