external/mambo: rename env var PMEM_MODES to PMEM_MODE

This patch just renames the env var to be non-plural to match PMEM_DISK.

A related patch going in to mambo will make the actual mode used in
mambo be called "private" instead of "cow" to reflect the fact that
you're getting a private copy of the image file and that any data
written to it will be lost when mambo exits. Unlike the old bogusdisk
driver, there is no separate .cow file where the writes go.

Signed-off-by: Aaron Sawdey <acsawdey@linux.ibm.com>
Acked-by: Michael Neuling <mikey@neuling.org>
[oliver: fixed whitespace damage on the patch]
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

external/mambo/skiboot.tcl

@@ -301,8 +301,8 @@ if { [info exists env(PMEM_VOLATILE)] } {
     set pmem_sizes [split $env(PMEM_VOLATILE) ","]
 }
 set pmem_modes ""
-if { [info exists env(PMEM_MODES)] } {
-    set pmem_modes [split $env(PMEM_MODES) ","]
+if { [info exists env(PMEM_MODE)] } {
+    set pmem_modes [split $env(PMEM_MODE) ","]
 }
 set pmem_root [mysim of addchild $root_node "pmem" ""]
 mysim of addprop $pmem_root int "#address-cells" 2