lib: test_scanf: Remove pointless use of type_min() with unsigned types

sparse was producing warnings of the form:

 sparse: cast truncates bits from constant value (ffff0001 becomes 1)

There is no actual problem here. Using type_min() on an unsigned type
results in an (expected) truncation.

However, there is no need to test an unsigned value against type_min().
The minimum value of an unsigned is obviously 0, and any value cast to
an unsigned type is >= 0, so for unsigneds only type_max() need be tested.

This patch also takes the opportunity to clean up the implementation of
simple_numbers_loop() to use a common pattern for the positive and
negative test.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210525122012.6336-2-rf@opensource.cirrus.com