detect-iprep: fix memory leaks

detect-iprep: fix memory leaks

Loading rules with iprep keyword cause
memory leaks due to missing frees.

Direct leak of 8 byte(s) in 4 object(s) allocated from:
    #0 0x7f81c862bd28 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc1d28)
    #1 0x7f81c6afea69 in pcre_get_substring (/lib/x86_64-linux-gnu/libpcre.so.3+0x27a69)
    #2 0x43206f7420676e68  (<unknown module>)

SUMMARY: AddressSanitizer: 8 byte(s) leaked in 4 allocation(s).