Nokia RX-51: Update documentation about ext2/3/4

Since commit 25c5b6517854 ("Nokia RX-51: Do not try calling both ext2load
and ext4load") command ext4load is used for all ext2/3/4 fs variants.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/README.nokia_rx51 b/doc/README.nokia_rx51
index 7f22ed4..1be0775 100644
--- a/doc/README.nokia_rx51
+++ b/doc/README.nokia_rx51
@@ -44,8 +44,7 @@
    * 1.2 find uImage on first fat partition
    * 1.3 find zImage on first fat partition
    * 1.4 same order for 2. - 4. fat partition
- * 2. same as 1. but for ext2/3 partition
- * 3. same as 1. but for ext4 partition
+ * 2. same as 1. but for ext2/3/4 partition
 
 
 Available additional commands/variables:
@@ -70,7 +69,7 @@
 
  * mmc ${mmcnum} (0 - external, 1 - internal)
  * partition number ${mmcpart} (1 - 4)
- * parition type ${mmctype} (fat, ext2, ext4)
+ * partition type ${mmctype} (fat, ext2, ext4; ext2 is just alias for ext4)
 
 Additional variables for booting kernel: