freebsd-update: Fix typo in comment

s/patchname expansion/pathname expansion/

Signed-off-by: a.biardi@tiscali.it
Pull-request: https://github.com/freebsd/freebsd-src/pull/1152
(cherry picked from commit 91811711625482f3a5778939e9999f53a0bea22a)
(cherry picked from commit 507e18dfc32491d2617488b470c2208db88977e2)