Convert pnmatch to single element array in regexec calls

The regexec function is declared as taking an array of regmatch_t
elements, and passing in the pointer to singleton element, while
correct, triggers a Coverity warning. Convert the singleton into
an array of one to silence the warning.

Reported by: Coverity
Coverity CID: 1009732, 1009733
MFC after: 2 weeks