arm64: Fix a logic bug in is_load_instr().

Logical and ('&&') was used to join two conditions instead of logical
or ('||') causing some store instructions to not be recognized.

Reported by: GCC 9 -Wparentheses

Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D31949

(cherry picked from commit 8753039a8f231ab04c7f3db9eaa5d9144d73440d)