gpu: host1x: fix uninitialized variable use

The error handling for platform_get_irq() failing no longer
works after a recent change, clang now points this out with
a warning:

drivers/gpu/host1x/dev.c:520:6: error: variable 'syncpt_irq' is uninitialized when used here [-Werror,-Wuninitialized]
        if (syncpt_irq < 0)
            ^~~~~~~~~~

Fix this by removing the variable and checking the correct
error status.

Fixes: 625d4ffb ("gpu: host1x: Rewrite syncpoint interrupt handling")
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20230127221418.2522612-1-arnd@kernel.org