avro

AVRO-3957: [C] Fix typos in docs and examples (#2795)

* AVRO-3957: [C] Fix misformatted type in docs

Signed-off-by: Sahil Kang <sahil.kang@asilaycomputing.com>
Signed-off-by: Sahil Kang <sahilkang@google.com>

* AVRO-3957: [C] Fix type in quickstop example

This removes the following warning:

  avro/lang/c/examples/quickstop.c:123:40: warning: incompatible pointer types passing 'int32_t **' (aka 'int **') to parameter of type
        'const char **' [-Wincompatible-pointer-types]
                          avro_value_get_string(&first_value, &p, &size);

Signed-off-by: Sahil Kang <sahil.kang@asilaycomputing.com>
Signed-off-by: Sahil Kang <sahilkang@google.com>

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Signed-off-by: Sahil Kang <sahil.kang@asilaycomputing.com>
Signed-off-by: Sahil Kang <sahilkang@google.com>