tools: ynl: correct typo and docstring

Correct typo in SpecAttr docstring. Changed SpecSubMessageFormat
docstring.
Signed-off-by: Alessandro Marcolini <alessandromarcolini99@gmail.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/6ab1dea7fb1f635c0d8b237f03a49eaa448c2bf4.1706962013.git.alessandromarcolini99@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/nlspec.py

@@ -144,7 +144,7 @@ class SpecEnumSet(SpecElement):
 
 
 class SpecAttr(SpecElement):
-    """ Single Netlink atttribute type
+    """ Single Netlink attribute type
 
     Represents a single attribute type within an attr space.
 
@@ -308,10 +308,9 @@ class SpecSubMessage(SpecElement):
 
 
 class SpecSubMessageFormat(SpecElement):
-    """ Netlink sub-message definition
+    """ Netlink sub-message format definition
 
-    Represents a set of sub-message formats for polymorphic nlattrs
-    that contain type-specific sub messages.
+    Represents a single format for a sub-message.
 
     Attributes:
         value         attribute value to match against type selector