nfp: fix clang -Wformat warnings

nfp: fix clang -Wformat warnings

When building with Clang we encounter these warnings:
| drivers/net/ethernet/netronome/nfp/nfp_app.c:233:99: error: format
| specifies type 'unsigned char' but the argument has underlying type
| 'unsigned int' [-Werror,-Wformat] nfp_err(pf->cpp, "unknown FW app ID
| 0x%02hhx, driver too old or support for FW not built in\n", id);
-
| drivers/net/ethernet/netronome/nfp/nfp_main.c:396:11: error: format
| specifies type 'unsigned char' but the argument has type 'int'
| [-Werror,-Wformat] serial, interface >> 8, interface & 0xff);

Correct format specifier for `id` is `%x` since the default type for the
`nfp_app_id` enum is `unsigned int`. The second warning is also solved
by using the `%x` format specifier as the expressions involving
`interface` are implicity promoted to integers (%x is used to maintain
hexadecimal representation).

Link: https://github.com/ClangBuiltLinux/linux/issues/378
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20220712000152.2292031-1-justinstitt@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>