Fix a trivial incorrect usage of variable argument macros detected
by Coverity (missing_va_end: va_end was not called for ap).

Fixes: Coverity CID 1446720 (VARARGS)
Fixes: e3c00c2e ("Hexagon (target/hexagon) opcode data structures")
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20210223111253.2831285-1-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>