drm/format-helper: Use KUNIT_EXPECT_MEMEQ macro

Commit b8a926be ("kunit: Introduce KUNIT_EXPECT_MEMEQ and
KUNIT_EXPECT_MEMNEQ macros") introduced a new macro to compare blocks of
memory and, if the test fails, print the result in a human-friendly
format. Therefore, use KUNIT_EXPECT_MEMEQ to compare memory blocks in
replacement of the KUNIT_EXPECT_EQ macro.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130125554.363481-1-mairacanal@riseup.net