OvmfPkg/Qemu: Fix various typos

Fix various typos in comments and documentation.

When "VbeShim.asm" is modified, we have to re-run "VbeShim.sh"
to update "VbeShim.h".
The string modified by this patch is only used when the DEBUG
macro (at the top of the file) is commented out. Since the
string is not referenced, NASM eliminates it, resulting in
the same byte array content in "VbeShim.h".

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Antoine Coeur <coeur@gmx.fr>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>
Message-Id: <20200207010831.9046-58-philmd@redhat.com>

OvmfPkg/Library/QemuBootOrderLib/QemuBootOrderLib.c

@@ -412,7 +412,7 @@ typedef struct {
                           If the call doesn't succeed, the contents of this
                           structure is indeterminate.
 
-  @param[out]    IsFinal  In case of successul parsing, this parameter signals
+  @param[out]    IsFinal  In case of successful parsing, this parameter signals
                           whether the node just parsed is the final node in the
                           device path. The call after a final node will attempt
                           to start parsing the next path. If the call doesn't