verify: use 'cmp_pattern' from 'lib/pattern.c' to compare pattern and buffer

verify: use 'cmp_pattern' from 'lib/pattern.c' to compare pattern and buffer

'cmp_pattern' function should be faster, since it does not use loops
and while doing 'memcmp' the same CPU cache line is used.

Keep in mind, that now single-byte pattern becomes the string of 512 bytes.
In that case this optimization will not work as expected, since 'memcmp'
will be called twice for the whole pattern, but in next patches this
behaviour will be avoided and single-byte pattern will stay single-byte
pattern without any attempt to duplicate it.

Also print buffer and pattern bytes as unsigned chars.

Signed-off-by: Roman Pen <r.peniaev@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>