firmware: arm_ffa: Fix NULL dereference in ffa_partition_info_get()

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.

Fixes: d0c0bce83122 ("firmware: arm_ffa: Setup in-kernel users of FFA partitions")
Signed-off-by: Unnathi Chalicheemala <unnathi.chalicheemala@oss.qualcomm.com>
Link: https://patch.msgid.link/20260617-ffa_partition_nullptr_fix-v2-1-bc801b4ce34c@oss.qualcomm.com
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>