PNOR: Check if the pnor mtd is already attached.

- In the pnor ubi attach function, check if the
  pnor is already attached to ubi, since a second
  attempt may fail.

Resolves openbmc/openbmc#2074

Change-Id: Ic07d56c5f656d4a236d85fd77acc9aef214a9c3b
Signed-off-by: Saqib Khan <khansa@us.ibm.com>
1 file changed