proc: rename "catch" function argument

"catch" is reserved keyword in C++, rename it to something both gcc and
g++ accept.

Rename "ign" for symmetry.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200331210905.GA31680@avx2


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>