Staging: irda: drivers: Replace (skb == NULL) with (!skb)

Some functions return NULL as an indication of failure.
The style (!skb) is more common than (skb == NULL) for these
functions.

Found by the following Coccinelle script.

@@
identifier i;
statement S;
@@

i = (\(kmalloc\|devm_kzalloc\|kmalloc_array\|devm_ioremap\|usb_alloc_urb\|
alloc_netdev\|dev_alloc_skb\)(...));

(
-if (i == NULL)
+if (!i)
S
|
-if (NULL == i)
+if (!i)
S
)

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>