CLEANUP: quic: remove a useless CRYPTO frame variable assignment

CLEANUP: quic: remove a useless CRYPTO frame variable assignment

This modification should have arrived with this commit:

	MINOR: quic: remove ->offset qf_crypto struct field

Since this commit, the CRYPTO offset node key assignment is done at parsing time
when calling qc_parse_frm() from qc_parse_pkt_frms().

This useless assigment has been reported in GH #3095 by coverity.

This patch should be easily backported as far as 2.6 as the one mentioned above
to ease any further backport to come.