pcmcia: Add error handling for add_interval() in do_validate_mem()

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

pcmcia: Add error handling for add_interval() in do_validate_mem()

In the do_validate_mem(), the call to add_interval() does not handle errors. If kmalloc() fails in add_interval(), it could result in a null pointer being inserted into the linked list, leading to illegal memory access when sub_interval() is called next.

This patch adds an error handling for the add_interval(). If add_interval() returns an error, the function will return early with the error code.