sh: checksum: add missing linux/uaccess.h include

SuperH does not include uaccess.h, even tho it calls access_ok().

Fixes: 68f4eae781dd ("net: checksum: drop the linux/uaccess.h include")
Reviewed-by: Simon Horman <[e-mail]>
Tested-by: Simon Horman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

arch/sh/include/asm/checksum_32.h

···
  */
 
 #include <linux/in6.h>
+#include <linux/uaccess.h>
 
 /*
  * computes the checksum of a memory block at buff, length len,