checkpatch: fix a typo in the regex for $allocFunctions

Here, we look for function such as 'netdev_alloc_skb_ip_align', so a '_'
is missing in the regex.

To make sure:
   grep -r --include=*.c skbip_a * | wc   ==>   0 results
   grep -r --include=*.c skb_ip_a * | wc  ==> 112 results

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Joe Perches <joe@perches.com>
Link: http://lkml.kernel.org/r/20200407190029.892-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -479,7 +479,7 @@ our $allocFunctions = qr{(?x:
 		(?:kv|k|v)[czm]alloc(?:_node|_array)? |
 		kstrdup(?:_const)? |
 		kmemdup(?:_nul)?) |
-	(?:\w+)?alloc_skb(?:ip_align)? |
+	(?:\w+)?alloc_skb(?:_ip_align)? |
 				# dev_alloc_skb/netdev_alloc_skb, et al
 	dma_alloc_coherent
 )};