powerpc/spider-pci: Remove set but not used variable 'val'

Fixes gcc '-Wunused-but-set-variable' warning:
# WARNING: Fixes tag on line 3 doesn't match correct format
# WARNING: Fixes tag on line 3 doesn't match correct format
# WARNING: Fixes tag on line 3 doesn't match correct format
# WARNING: Fixes tag on line 3 doesn't match correct format
# WARNING: Fixes tag on line 3 doesn't match correct format
# WARNING: Fixes tag on line 3 doesn't match correct format

arch/powerpc/platforms/cell/spider-pci.c: In function 'spiderpci_io_flush':
arch/powerpc/platforms/cell/spider-pci.c:28:6: warning:
variable ‘val’ set but not used [-Wunused-but-set-variable]

It never used since introduction.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210601085319.140461-1-libaokun1@huawei.com