Cleanup: zap_leaf_array_read() should use BSWAP_64()

We neuter the byteswap macros in Coverity builds to suppress Coverity
complaints about byteswapped data being tainted. However, this does not
apply to functions that hardcode byteswapping such as
`zap_leaf_array_read()`. We modify `zap_leaf_array_read()` to use
`BSWAP_64()`. This suppresses Coverity's complaints and makes the code
slightly more succinct.

Reported-by: Coverity (CID 1524543)
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>

module/zfs/zap_leaf.c

@@ -288,13 +288,9 @@ zap_leaf_array_read(zap_leaf_t *l, uint16_t chunk,
 	/* Fast path for one 8-byte integer */
 	if (array_int_len == 8 && buf_int_len == 8 && len == 1) {
 		struct zap_leaf_array *la = &ZAP_LEAF_CHUNK(l, chunk).l_array;
-		uint8_t *ip = la->la_array;
 		uint64_t *buf64 = buf;
 
-		*buf64 = (uint64_t)ip[0] << 56 | (uint64_t)ip[1] << 48 |
-		    (uint64_t)ip[2] << 40 | (uint64_t)ip[3] << 32 |
-		    (uint64_t)ip[4] << 24 | (uint64_t)ip[5] << 16 |
-		    (uint64_t)ip[6] << 8 | (uint64_t)ip[7];
+		*buf64 = BSWAP_64(*(uint64_t *)la->la_array);
 		return;
 	}