cassini: Fix a memory leak in the error handling path of cas_init_one()

In the Linux kernel, the following vulnerability has been resolved:

cassini: Fix a memory leak in the error handling path of cas_init_one()

cas_saturn_firmware_init() allocates some memory using vmalloc(). This

memory is freed in the .remove() function but not it the error handling

path of the probe.

Add the missing vfree() to avoid a memory leak, should an error occur.