kunit: don't show `1 == 1` in failed assertion messages

Currently, given something (fairly dystopian) like
> KUNIT_EXPECT_EQ(test, 2 + 2, 5)

KUnit will prints a failure message like this.
>  Expected 2 + 2 == 5, but
>      2 + 2 == 4
>      5 == 5

With this patch, the output just becomes
>  Expected 2 + 2 == 5, but
>      2 + 2 == 4

This patch is slightly hacky, but it's quite common* to compare an
expression to a literal integer value, so this can make KUnit less
chatty in many cases. (This patch also fixes variants like
KUNIT_EXPECT_GT, LE, et al.).

It also allocates an additional string briefly, but given this only
happens on test failures, it doesn't seem too bad a tradeoff.
Also, in most cases it'll realize the lengths are unequal and bail out
before the allocation.

We could save the result of the formatted string to avoid wasting this
extra work, but it felt cleaner to leave it as-is.

Edge case: for something silly and unrealistic like
> KUNIT_EXPECT_EQ(test, 4, 5);

It'll generate this message with a trailing "but"
>  Expected 4 == 5, but
>  <next line of normal output>

It didn't feel worth adding a check up-front to see if both sides are
literals to handle this better.

*A quick grep suggests 100+ comparisons to an integer literal as the
right hand side.

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>