fs/proc/inode.c: delete unnecessary variable in proc_alloc_inode()

Link: http://lkml.kernel.org/r/20181203164015.GA6904@avx2


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>