stdio-common: Fix error reporting in scanf input specifier tests

stdio-common: Fix error reporting in scanf input specifier tests

Remove buffer contents reporting from the real variant of 'verify_input'
where there has been an input data format error making the contents of
data buffers irrelevant.

For example given invalid float input data:

%a:nan:1:3:nan(:

these messages are produced:

error: ./tst-scanf-format-skeleton.c:240: input buffer: `0000c07f'
error: ./tst-scanf-format-skeleton.c:240: value buffer: `0000c07f'
error: ./tst-scanf-format-skeleton.c:242: input line 1: input data format error

with the two former lines irrelevant.  Remove them from output then,
only leaving:

error: ./tst-scanf-format-skeleton.c:242: input line 1: input data format error

No test case added as it's a test case issue in the first place.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>