rx: remove rx_misc.h define trailing semicolons

PIN and UNPIN macro definitions should not have trailing
semicolons.

Change-Id: I242c0a7a40cbabe852ed975eb64df52dbb585624
Reviewed-on: http://gerrit.openafs.org/9088
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Simon Wilkinson <simonxwilkinson@gmail.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>