drivers/net/irda: Eliminate memory leak

dev_alloc_skb allocates some memory, so that memory should be freed before
leaving the function in an error case.

Corrected some typos in a nearby comment as well.

A simplified version of the semantic match that finds this problem is:
(http://coccinelle.lip6.fr/

)

// <smpl>
@r exists@
local idexpression x;
expression E;
identifier f1;
iterator I;
@@

x = dev_alloc_skb(...);
<... when != x
     when != true (x == NULL || ...)
     when != if (...) { <+...x...+> }
     when != I (...) { <+...x...+> }
(
 x == NULL
|
 x == E
|
 x->f1
)
...>
* return ...;
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>