x86: mtrr: Fix 'ensable' typo

Fix a typo in the command help.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/cmd/x86/mtrr.c b/cmd/x86/mtrr.c
index 084d731..5d25c58 100644
--- a/cmd/x86/mtrr.c
+++ b/cmd/x86/mtrr.c
@@ -135,5 +135,5 @@
 	"set <reg> <type> <start> <size>   - set a register\n"
 	"\t<type> is Uncacheable, Combine, Through, Protect, Back\n"
 	"disable <reg>      - disable a register\n"
-	"ensable <reg>      - enable a register"
+	"enable <reg>       - enable a register"
 );