selftests: arm64: Clarify output when verifying SVE register set

selftests: arm64: Clarify output when verifying SVE register set

When verifying setting a Z register via ptrace we check each byte by hand,
iterating over the buffer using a pointer called p and treating each
register value written as a test. This creates output referring to "p[X]"
which is confusing since SVE also has predicate registers Pn. Tweak the
output to avoid confusion here.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210913125505.52619-6-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>