Documentation: fix a typo for intel_iommu=nobounce

"untrusted" was mis-spelled as "unstrusted"
Signed-off-by: Alex Hung <alex.hung@canonical.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-parameters.txt

@@ -1775,7 +1775,7 @@
 			provided by tboot because it makes the system
 			vulnerable to DMA attacks.
 		nobounce [Default off]
-			Disable bounce buffer for unstrusted devices such as
+			Disable bounce buffer for untrusted devices such as
 			the Thunderbolt devices. This will treat the untrusted
 			devices as the trusted ones, hence might expose security
 			risks of DMA attacks.