Input: ipaq-micro-keys - add length check in micro_key_receive

Input: ipaq-micro-keys - add length check in micro_key_receive

The driver accesses the message payload (msg[0]) without checking if
the length is greater than zero. The parent MFD driver can produce a
payload with a length of 0, in which case msg[0] would be uninitialized
or stale.

Add a check to return early if len is less than 1.

Reported-by: sashiko-bot@kernel.org
Assisted-by: Antigravity:gemini-3.5-flash
Link: https://patch.msgid.link/aintAvTyw4CVb5hG@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>