swupdate.bbclass: drop suffix from class name

With commit [1] in bitbake the parsing of the swupdate-bbclass fails
with message:

    ERROR: ParseError at .../meta-swupdate/classes-recipe/swupdate.bbclass:36: Could not inherit file swupdate-common.bbclass

Remove the .bbclass suffix from the inherit statement to resolve this issue.
No other inherit statements seem to use suffix.

[1] https://git.openembedded.org/bitbake/commit/?id=f7c55c8147329670fd5bc55b1ae3f47f25b89bab

Signed-off-by: Peter Bergin <peter@berginkonsult.se>

classes/swupdate.bbclass

@@ -33,7 +33,7 @@
 #   corresponding image files cannot be found in the ${DEPLOY_DIR_IMAGE} folder, an
 #   image file with exactly the name as specified in SWUPDATE_IMAGES is searched for.
 
-inherit swupdate-common.bbclass
+inherit swupdate-common
 inherit image-artifact-names
 
 S = "${WORKDIR}/${PN}"