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")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>