tools: ipxe: update for fixing build with GCC9

tools: ipxe: update for fixing build with GCC9

Building with GCC9 (on openSUSE Tubmleweed) generates a lot of errors of
the "taking address of packed member of ... may result in an unaligned
pointer value" kind.

Updating to upstream commit 1dd56dbd11082 ("[build] Workaround compilation
error with gcc 9.1") seems to fix the problem.

For more info, see:

https://git.ipxe.org/ipxe.git/commit/1dd56dbd11082fb622c2ed21cfaced4f47d798a6

Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
Acked-by: Wei Liu <wl@xen.org>