mdadm: sysfs.c fix coverity issues

mdadm: sysfs.c fix coverity issues

Fixing the following coding errors the coverity tools found:

* Event fixed_size_dest: You might overrun the 32-character
fixed-size string "mdi->sys_name" by copying "devnm" without
checking the length

* Event fixed_size_dest: You might overrun the 50-character
fixed-size string "sra->text_version" by copying "buf + 9"
without checking the length.

* Event string_overflow: You might overrun the 32-character
destination string "dev->sys_name" by writing 256 characters
from "de->d_name".

Signed-off-by: Nigel Croxon <ncroxon@redhat.com>