parse: fix parse_is_percent() warning

parse: fix parse_is_percent() warning

When compiling an out of tree ioengine, such as the SPDK fio plugin,
which has -Wextra in CFLAGS, the compiler gives the following warning:

parse.h: In function ‘parse_is_percent’:
parse.h:134:13: warning: comparison of integer expressions of different signedness: ‘long long unsigned int’ and ‘int’ [-Wsign-compare]

Since this warning was introduced recently by fio
commit b75c0fae6612 ("parse: simplify parse_is_percent()"),
and since this is the only warning seen when compiling the SPDK fio
plugin, readd the ULL prefix to parse_is_percent().

Fixes: b75c0fae6612 ("parse: simplify parse_is_percent()")
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>