MIPS: lantiq: Explicitly compare LTQ_EBU_PCC_ISTAT against 0

MIPS: lantiq: Explicitly compare LTQ_EBU_PCC_ISTAT against 0

When building xway_defconfig with clang:

arch/mips/lantiq/irq.c:305:48: error: use of logical '&&' with constant
operand [-Werror,-Wconstant-logical-operand]
        if ((irq == LTQ_ICU_EBU_IRQ) && (module == 0) && LTQ_EBU_PCC_ISTAT)
                                                      ^ ~~~~~~~~~~~~~~~~~
arch/mips/lantiq/irq.c:305:48: note: use '&' for a bitwise operation
        if ((irq == LTQ_ICU_EBU_IRQ) && (module == 0) && LTQ_EBU_PCC_ISTAT)
                                                      ^~
                                                      &
arch/mips/lantiq/irq.c:305:48: note: remove constant to silence this
warning
        if ((irq == LTQ_ICU_EBU_IRQ) && (module == 0) && LTQ_EBU_PCC_ISTAT)
                                                     ~^~~~~~~~~~~~~~~~~~~~
1 error generated.

Explicitly compare the constant LTQ_EBU_PCC_ISTAT against 0 to fix the
warning. Additionally, remove the unnecessary parentheses as this is a
simple conditional statement and shorthand '== 0' to '!'.

Fixes: 3645da0276ae ("OF: MIPS: lantiq: implement irq_domain support")
Link: https://github.com/ClangBuiltLinux/linux/issues/807
Reported-by: Dmitry Golovin <dima@golovin.in>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>