arm64: csum: cast to the proper type

The last line of ip_fast_csum() calls csum_fold(), forcing the
type of the argument passed to be u32. But csum_fold() takes a
__wsum argument (which is __u32 __bitwise for arm64). As long
as we're forcing the cast, cast it to the right type.

Signed-off-by: Alex Elder <[e-mail]>
Acked-by: Robin Murphy <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

arch/arm64/include/asm/checksum.h

···
 	} while (--n > 0);
 
 	sum += ((sum >> 32) | (sum << 32));
-	return csum_fold((__force u32)(sum >> 32));
+	return csum_fold((__force __wsum)(sum >> 32));
 }
 #define ip_fast_csum ip_fast_csum