ipc/mqueue.c: delete an unnecessary check before the macro call dev_kfree_skb()

ipc/mqueue.c: delete an unnecessary check before the macro call dev_kfree_skb()

dev_kfree_skb() input parameter validation, thus the test around the call
is not needed.

This issue was detected by using the Coccinelle software.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Markus Elfring <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Manfred Spraul <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>