etnaviv: fix texture_format_needs_swiz

memcmp returns 0 when both swizzles are the same, which means we don't
need any hardware swizzling. texture_format_needs_swiz should return
true when the return value of the memcmp is non-zero.

Fixes: 751ae6af ("etnaviv: add support for swizzled texture formats")
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Marek Vasut <marex@denx.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Wladimir J. van der Laan <laanwj@gmail.com>
(cherry picked from commit 52e93e30)