mtd: physmap_of: fix incorrect check

This patch fixes a spelling error that has resulted from copy and
pasting. The location of the error was found using a semantic patch
but the semantic patch was not trying to find these errors. After
looking things over it seemed logical that this change was needed.

The patch also makes sure mtd_list is not being freed if it has not
been allocated

Signed-off-by: Stoyan Gaydarov <sgayda2@uiuc.edu>
Signed-off-by: Vimal Singh <vimalsingh@ti.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>