mtd: cfi_cmdset_0002: don't free cfi->cfiq in error path of cfi_amdstd_setup()

Else there may be a double-free problem, because cfi->cfiq will
be freed by mtd_do_chip_probe() if both the two invocations of
check_cmd_set() return failure.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>