oem-factory-reset: Fix index used for default boot option

Since we sort the boot options prior to selecting the new default entry,
we need to use the index of the entry in the list prior to being sorted,
vs always setting it as 1. This fixes setting/booting of the default
OS target where the list entries are changed when calling sort.

Test: perform OEM factory reset with Fedora 32 installed, verify
default boot succeeds followng reset.

Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>

initrd/bin/oem-factory-reset

@@ -221,8 +221,11 @@ set_default_boot_option()
     # clear existing default configs
     rm "/boot/kexec_default.*.txt" 2>/dev/null
 
+    # get correct index for entry
+    index=$(grep -n "$entry" $option_file | cut -f1 -d ':')
+
     # write new config
-    echo "$entry" > /boot/kexec_default.1.txt
+    echo "$entry" > /boot/kexec_default.$index.txt
 
     # validate boot option
     cd /boot && /bin/kexec-boot -b "/boot" -e "$entry" -f \