mm: in_irq() cleanup

Replace the obsolete and ambiguos macro in_irq() with new macro
in_hardirq().

Link: https://lkml.kernel.org/r/20210813145245.86070-1-changbin.du@gmail.com


Signed-off-by: Changbin Du <changbin.du@gmail.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>	[kmemleak]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>