firmware: arm_ffa: Fix NULL dereference in ffa_partition_info_get()

In the Linux kernel, the following vulnerability has been resolved: firmware: arm_ffa: Fix NULL dereference in ffa_partition_info_get() ffa_partition_info_get() passes uuid_str directly to uuid_parse() without a NULL check. When a caller passes NULL, uuid_parse() -> __uuid_parse() -> uuid_is_valid() dereferences the pointer, causing a kernel panic: | Unable to handle kernel NULL pointer dereference at virtual address | 0000000000000040 | pc : uuid_parse+0x40/0xac | lr : ffa_partition_info_get+0x1c/0x94 [arm_ffa] Add a NULL guard before uuid_parse() so a NULL argument returns -ENODEV instead of crashing. Callers are expected to always supply a valid partition UUID, so NULL is not a supported input.