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

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.

Fixes: 7b4884ca8853 ("pcmcia: validate late-added resources")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>