wifi: iwlwifi: mvm: fix clang -Wformat warnings

When building with Clang we encounter these warnings:
| drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c:1108:47: error:
| format specifies type 'unsigned char' but the argument has type 's16'
| (aka 'short') [-Werror,-Wformat] IWL_DEBUG_INFO(mvm, "\tburst index:
| %hhu\n", res->ftm.burst_index);
-
| drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c:1111:47: error:
| format specifies type 'unsigned char' but the argument has type 's32'
| (aka 'int') [-Werror,-Wformat] IWL_DEBUG_INFO(mvm, "\trssi spread:
| %hhu\n", res->ftm.rssi_spread);

The previous format specifier `%hhu` describes a u8 but our arguments
are wider than this which means bits are potentially being lost.

Variadic functions (printf-like) undergo default argument promotion.
Documentation/core-api/printk-formats.rst specifically recommends using
the promoted-to-type's format flag.

As per C11 6.3.1.1:
(https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf) `If an int
can represent all values of the original type ..., the value is
converted to an int; otherwise, it is converted to an unsigned int.
These are called the integer promotions.` Thus it makes sense to change
`%hhu` to `%d` for both instances of the warning.

Link: https://github.com/ClangBuiltLinux/linux/issues/378
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220711222919.2043613-1-justinstitt@google.com