kselftest/arm64: mte: fix printf type warnings about __u64

kselftest/arm64: mte: fix printf type warnings about __u64

When printing the signal context's PC, we use a "%lx" format specifier,
which matches the common userland (glibc's) definition of uint64_t as an
"unsigned long". However the structure in question is defined in a
kernel uapi header, which uses a self defined __u64 type, and the arm64
kernel headers define this using "int-ll64.h", so it becomes an
"unsigned long long". This mismatch leads to the usual compiler warning.

The common fix would be to use "PRIx64", but because this is defined by
the userland's toolchain libc headers, it wouldn't match as well. Since
we know the exact type of __u64, just use "%llx" here instead, to silence
this warning.

This also fixes a more severe typo: "$lx" is not a valid format
specifier.

Fixes: 191e678bdc9b ("kselftest/arm64: Log unexpected asynchronous MTE faults")
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240816153251.2833702-7-andre.przywara@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>