EmulatorPkg: Fix spelling mistake for occurred

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2361

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Guomin Jiang <guomin.jiang@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>

EmulatorPkg/TimerDxe/Timer.c

@@ -301,7 +301,7 @@ Returns:
 
   EFI_OUT_OF_RESOURCES  - Not enough resources available to initialize driver.
 
-  EFI_DEVICE_ERROR      - A device error occured attempting to initialize the driver.
+  EFI_DEVICE_ERROR      - A device error occurred attempting to initialize the driver.
 
 **/
 {