HID: picolcd: prevent NULL pointer dereference in picolcd_send_and_wait()

HID: picolcd: prevent NULL pointer dereference in picolcd_send_and_wait()

In picolcd_send_and_wait(), an integer overflow of the signed loop counter
'k' can theoretically lead to a NULL pointer dereference of 'raw_data'.
If the loop executes more than INT_MAX times, 'k' becomes negative,
making the condition 'k < size' true even when 'size' is 0.

Change the type of 'k' to 'unsigned int' to prevent the overflow and
eliminate the out-of-bounds access.

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

[jkosina@suse.com: extended hash length]
Fixes: fabdbf2fd22fa17 ("HID: picoLCD: split driver code")
Signed-off-by: Georgiy Osokin <g.osokin@auroraos.dev>
Signed-off-by: Jiri Kosina <jkosina@suse.com>