tests/qtest/ast2700-smc-test: Fix leak

tests/qtest/ast2700-smc-test: Fix leak

ASAN spotted a leak of the memory used to hold the tmp_path:

Direct leak of 35 byte(s) in 1 object(s) allocated from:
    #0 0x55e29aa96da9 in malloc ../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:69:3
    #1 0x7fe0cfb26518 in g_malloc ../glib/gmem.c:106
    #2 0x7fe0cfb4146e in g_strconcat ../glib/gstrfuncs.c:629
    #3 0x7fe0cfb0a78f in g_get_tmp_name ../glib/gfileutils.c:1742
    #4 0x7fe0cfb0b00b in g_file_open_tmp ../glib/gfileutils.c:1802
    #5 0x55e29ab53961 in test_ast2700_evb ../tests/qtest/ast2700-smc-test.c:20:10
    #6 0x55e29ab53803 in main ../tests/qtest/ast2700-smc-test.c:65:5
    #7 0x7fe0cf7bd24c in __libc_start_main ../csu/libc-start.c:308
    #8 0x55e29a9f7759 in _start ../sysdeps/x86_64/start.S:120

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Jamin Lin <jamin_lin@aspeedtech.com>
Message-ID: <20250509175047.26066-1-farosas@suse.de>
Signed-off-by: Cédric Le Goater <clg@redhat.com>